The term Vistula Veneti (or Baltic Veneti) has been used in modern times to distinguish the Veneti noted by Greek and Roman geographers along the Vistula and the Bay of Gdańsk from other tribes around them and other tribes of the same name elsewhere such as the Adriatic Veneti (about the same area of today's Veneto), the Veneti of Bretagne, and the so-called Paphlagonian Veneti (of, today's, northern Turkey coast). They are one of the tribes that are suspected as the ancestors of some or all of today's Slavs.
Early historical sources
Roman authors saw the lands between the Rhine and the Vistula rivers as Germania. East of the Vistula was classed as Sarmatia. The earliest source that refers to Veneti in Central Europe as the "Vennones" and as members of the "Vindelici" is Strabo locating them, at the turn of the millennium, north of Italy along Lake Constance (previously known as Lake Veneti) and recalling a campaign and a lake battle conducted against them by Drusus and Tiberius. He also speculates that the Veneti may have settled in Venice and migrated north into Italy. Pliny the Elder places the Veneti along the Baltic coast. He calls them the Sarmatian Venedi (Latin Sarmatae Venedi). Thereafter, the 2nd-century Greek-Roman geographer Ptolemy, in his section on Sarmatia, places the Greater Vouenedai along the entire Venedic Bay, which can be located from the context on the southern shores of the Baltic. He names tribes south of these Greater Venedae both along the eastern bank of the Vistula and further east.
The most exhaustive Roman treatment of the Veneti comes in Germania by Tacitus, who, writing in AD 98, locates the Veneti among the peoples on the eastern fringe of Germania. He was uncertain of their ethnic identity, classifying them as Germans based on their way of life but not based on their language (in comparison to, for example, the Peucini):
Here Suebia ends. I do not know whether to class the tribes of the Peucini, Venedi, and Fenni with the Germans or with the Sarmatians. The Peucini, however, who are sometimes called Bastarnae, are like Germans in their language, manner of life, and mode of settlement and habitation. Squalor is universal among them and their nobles are indolent. Mixed marriages are giving them something of the repulsive appearance of the Sarmatians... The Veneti have borrowed largely from Sarmatian ways; their plundering forays take them all over the wooded and mountainous country that rises between the Peucini and the Fenni. Nevertheless, they are to be classed as Germani, for they have settled houses, carry shields and are fond of travelling fast on foot; in all these respects they differ from the Sarmatians, who live in wagons or on horseback.
Despite this rather "functional" accounting of the Veneti as belonging amongst the Germanic tribes, slavists such as Pavel Josef Šafařík have criticized Tacitus for identifying the Venethi as Germanic, due to the similar appearance of Slavs and Germans.[unreliable source?]
Among the Byzantine authors, the Gothic author Jordanes in his work Getica (written in 550 or 551 AD). describes the Veneti as a "populous nation" whose dwellings begin at the sources of the Vistula and occupy "a great expanse of land." He describes them as the ancestors also of the Sclavenes (a people who appeared on the Byzantine frontier in the early 500s and who are believed to have been the early Southern Slavs) and of the Antes. Specifically, he states that the Slavs and the Antes used to be called the Veneti but are now "chiefly" (though, by implication, not exclusively) called Slavs and Antes. He places the Slavs north of a line from the Dniestr to Lake Musianus the location of which is unclear but which has been variously identified with Lake Constance, the Tisa-Danube marshes or the Danube delta. He places the Antes to the east of the Slavs.
Later in Getica he returns to the Veneti stating, again, that though "off-shoots of one stock [these people] have now three names, that is Veneti, Antes and Sclaveni" and noting that they, at one time, had been conquered by the Goths under Ermanaric. Consistent with the view that the Veneti were an umbrella term for these three peoples, he later also recalls the defeat of the Antes at the hands of a Gothic chieftain named Vinitharius, i.e., conqueror of the Veneti.
Though Jordanes is the only author to explicitly associate the Veneti with what appear to have been Slavs and Antes, the Tabula Peutingeriana, originating from the 3rd-4th century AD, separately mentions the Venedi on the northern bank of the Danube somewhat upstream of its mouth, and the Venadi Sarmatae along the Baltic coast.
Henry of Livonia in his Latin chronicle of c. 1200 described a tribe of the Vindi (German Winden, English Wends) that lived in Courland and Livonia in what is now Latvia. The tribe’s name is preserved in the river Windau (Latvian Venta), with the town of Windau (Latvian Ventspils) at its mouth, and in Wenden, the old name of the town of Cēsis in Livonia. The fact that 12th century Germans from Saxony referred to these people as 'Winden' suggests that they were Slavs.  (See Vends).
During the Middle Ages the region east of the Vistula was inhabited by people speaking Old Prussian, a now-extinct Baltic language. It is unknown what language the Veneti spoke, although the implication of Tacitus' description of them is that it was not a form of Germanic.
It has been argued that the Veneti were a centum Indo-European people, rather than satem Baltic-speakers. Zbigniew Gołąb considers that the hydronyms of the Vistula and Odra river basins had a North-West Indo-European character with close affinities to the Italo-Celtic branch, but different from the Germanic branch, and show resemblances to those attested in the area of the Adriatic Veneti (in Northeastern Italy) as well as those attested in the Western Balkans that are attributed to Illyrians, which suggests points to a possible connection between these ancient Indo-European peoples.
In the region identified by Ptolemy and Pliny, east of the Vistula and adjoining the Baltic, there was an Iron Age culture, known to archaeologists as the West Baltic Cairns Culture or West Baltic Barrow Culture, shown coloured violet on the map given here. The culture is associated with the Proto-Balts, who kept this area for almost two thousand years, avoiding adoption of new ideas from their neighbours. These herders lived in small settlements or in little lake dwellings built on artificial islands made of several layers of wooden logs attached by stakes. Their metals were imported, and their dead were cremated and put in urns covered by small mounds.
In the Post-War era Polish archaeologists generally interpreted the Veneti as the possible bearers of the Pomeranian culture, an Iron Age archaeological culture in Poland, including, to the west of the Vistula. Although still preponderant, this west-of-Vistula hypotheses has been rejected by one Polish author,
Relation between the Veneti, the Slavs, and the Balts
Based on the above sources, the Veneti in antiquity were geographically contiguous to and coterminous with the various early Germanic peoples.
It is also clear that the Franks (see, e.g., Life of Saint Martinus, Fredegar's Chronicle, Gregory of Tours), Lombards (see, e.g., Paul the Deacon), and Anglo-Saxons (see Widsith's Song) referred to Slavs both in the Elbe-Saal region and in Pomerania generally, as Wenden or Winden (see Wends). Likewise, the Franks and Bavarians of Styria and Carinthia referred to their Slavic neighbours as Windische.
It has not been show that either the original Veneti or the Slavs themselves used the ethnonym Veneti to describe their ethos (though they have used the term "Zlo-wene"). Of course, other peoples, e.g., the Germans (called so first by the Romans), did not have a name for themselves other than localized tribal names.
Considering Ptolemy's Ouenedai and their location along the Baltic sea, a German linguist, Alexander M. Schenker, asserts that the vocabulary of the Slavic languages shows no evidence that the early Slavs were exposed to the sea. Schenker claims that Proto-Slavic had no maritime terminology and further claims it even lacked a word for amber (but see "jantar" whose etymology is unclear and Polish "glaz" as in 'stone' or 'rock') which was the most important item of export from the shores of the Baltic to the Mediterranean. Based on this belief, and the fact that Ptolemy refers to the Baltic Sea as the "Venedic" Bay Schenker decides against a possible identification of the Veneti of Ptolemy's times, with today's Slavs. According to Gołąb, Schenker's conclusion is supported by the fact that to the east of the Venedae, Ptolemy mentions two further tribes called Stavanoi (Σταυανοί) and Souobenoi (Σουοβενοι), both of which have been interpreted as possibly the oldest historical attestations of at least some Slavs. 
On the other hand, others have interpreted these as Prussian tribes (Sudini) as they follow other known Prussian tribes in Ptolemy's listing (e.g., the Galindae (Γαλίνδαι)). Further, the Souobenoi (Σουοβενοι) occupied a small patch somewhere north of China.  Moreover, that conclusion (Gołąb, Schenker), if correct, may only account for the Byzantine Slavs of Jordanes and Procopius since Jordanes clearly (see above) understands Veneti as a group at least as broad as - today's - Slavs but does not understand the converse to be the case (i.e., his "Slavs" are localized around Byzantium and north through Moravia only) since his Slavs remain a subset of the broader category of Veneti. It also is clear that the Byzantine term "Slav" had gradually replaced the Germanic "Winden"/"Wenden" as applied to all the people we would, today, consider Slavs.
Linguists agree that Slavic languages evolved in close proximity with the Baltic languages. The two language families probably evolved from a common ancestor, a phylogenetic Proto-Balto-Slavic language continuum. The earliest origins of Slavs seem to lie in the area between the Middle Dnieper and the Bug rivers, where the most archaic Slavic hydronyms have been established. The vocabulary of Proto-Slavic had a heterogenous character and there is evidence that in the early stages of its evolution it adopted some loanwords from centum-type Indo-European languages. It has been proposed that contacts of Proto-Slavs with the Veneti may have been one of the sources for these borrowings. The aforementioned area of proto-Slavic hydronyms roughly corresponds with the Zarubintsy archeological culture which has been interpreted as the most likely locus of the ethnogenesis of Slavs. According to Polish archaeologist Michał Parczewski, Slavs began to settle in southeastern Poland no earlier than the late 5th century AD, the Prague culture being their recognizable expression.
Etymology of the ethnonym Veneti
According to Julius Pokorný, the ethnonym Venetī (singular *Venetos) is derived from Proto Indo-European root *u̯en-, venuto - veniti - venetici 'to arrive; to come from outside, to be a foreigner'. As shown by the comparative material, the Germanic languages may have had two terms of different origin: Old High German Winida 'Wende' points to Pre-Germanic *u̯enétos, while Lat.-Germ. Venedi (as attested in Tacitus) and Old English Winedas 'Wends' call for Pre-Germanic *u̯énetos.
The ethnonym would then be etymologically related to words as Latin venus, -eris 'love, passion, grace'; Sanskrit vanas- 'lust, zest', vani- 'wish, desire'; Old Irish fine (< Proto-Celtic *venjā) 'kinship, kinfolk, alliance, tribe, family'; Old Norse vinr, Old Saxon, Old High German wini, Old Frisian, Old English wine 'friend'.
Steinacher, incorrectly, states: "The name Veneder was introduced by Jordanes. The assumption that these were Slavs can be traced back to the 19th century to Pavel Josef Šafařík from Prague, who tried to establish a Slavic Origin history. Scholars and historians since then viewed the reports on Venedi/Venethi by Tacitus, Pliny and Ptolemy as the earliest historical attestation of Slavs. "Such conceptions, started in the 16th century, resurfaced in the 19th century where they provided the basis for interpretations of the history and origins of Slavs." 
On the other hand, in the 1980s and 1990s some Slovene scholars proposed a theory according to which the Veneti were Proto-Slavs and bearers of the Lusatian culture along the Amber Path who settled the region between the Baltic sea and Adriatic Sea, as presented in their book "Veneti - First Builders of European Community". This theory would place the Veneti as a pre-Celtic, pre-Latin and pre-Germanic population of Europe. The theory has been criticised and rejected by some Slovenian and other European scholars.
The Slavs, an eastern branch of the Indo-European family, were known to the Roman and Greek writers of the 1st and 2d centuries A.D. under the name of Venedi as inhabiting the region beyond the Vistula. ... In the course of the early centuries of our era the Slavs expanded in all directions, and by the 6th century, when they were known to Gothic and Byzantine writers as Sclaveni, they were apparently already separated into three main divisions: ...—An Encyclopedia of World History, William L. Langer, Harvard University, 1940 & 1948
- Strabo, "Geography", IV, ch IV.
- Pliny, Natural History, IV: 96-97.
- Ptolemy, Geography, III 5. 21.
- Tacitus, Germania, 46.
- Curta (2001, p. 7)
- Carleton S Coon. The Peoples of Europe. Chapter VI, Section 7 ‘’they (Slavs) were often confused with Germans’’
- Curta 2001: 38. Dzino 2010: 95.
- Getica 5
- Getica 23
- Getica 48
- Gołąb 1992: 287-291, 295-296.
- Alexander M. Schenker, The Dawn of Slavic: An Introduction to Slavic Philology (1995), 1.4., including a reference to J. Ochmański, Ochmański, Historia Litwy, 2nd ed. (Wrocław, 1982)
- Zbigniew Gołąb, The Origins of the Slavs: A Linguist's view (1992) pp. 888, 263-268
- Przemyslaw Urbanczyk, Iron Age Poland in Pam Crabtree and Peter Bogucki (eds), Ancient Europe, 8000 B.C. to A.D. 1000: An Encyclopedia of the Barbarian World (2004).
- Okulicz 1986; Pleterski 1995
- Andrzej Buko, The archaeology of early medieval Poland: discoveries - hypotheses - interpretations (2008)
- Gottfried Schramm Venedi, Antes, Sclaveni, Sclavi in Jahrbücher für Geschichte Osteuropas, Neue Folge, Bd. 43, Heft 2, 1995>
- Schenker 1996: 3-5
- Gołąb 1992: 291.
- Edward Luther Stevenson Translation of "Geography of Claudius Ptolemy"
- Jordanes, Getica 5
- Paul Barford, Early Slavs
- Gottfried Schramm Venedi, Antes, Sclaveni, Sclavi in Jahrbücher für Geschichte Osteuropas, Neue Folge, Bd. 43, Heft 2, 1995>
- Gołąb 1992: 300.
- Andersen 2003
- Gołąb 1992: 175; for detailed examples see p. 79-86.
- Parczewski 1993.
- Pokorny 1959: 1146 - 1147; Steinacher 2002: 33
- (PDF) http://donelaitis.vdu.lt/prussian/Elbin.pdf. Missing or empty
- Steinacher 2004; see also Origins of Vandals.
- Steinacher 2002: 31-35.
- Z. Skrbiš, 41-56 and M. Svašek, 144.
- Agnes, Michael (Editor in Chief) (1999). "Webster's New World College Dictionary". Cleveland: MacMillan USA, 1999. ISBN 0-02-863118-8.
- Andersen, Henning (2003), "Slavic and the Indo-European Migrations", Language contacts in prehistory: studies in stratigraphy, John Benjamins Publishing Company, ISBN 1-58811-379-5.
- Curta, Florin (2001). The Making of the Slavs. History and Archaeology of the Lower Danube Region, c. 500-700. Cambridge University Press, 2001.
- Dzino, Daniel (2010). Becoming Slav, Becoming Croat: Identity Transformations in Post-Roman and Early Medieval Dalmatia. Brill, 2010.
- Gołąb, Zbigniew (1992). The Origins of the Slavs: A Linguist's view. Columbus: Slavica Publishers, 1992. ISBN 0-89357-231-4.
- Krahe, Hans (1957). Vorgeschichtliche Sprachbeziehungen von den baltischen Ostseeländern bis zu den Gebieten um den Nordteil der Adria. Mainz: Akademie der Wissenschaften und der Literatur, 1957.
- Krahe, Hans (1954). Sprache und Vorzeit: Europäische Vorgeschichte nach dem Zeugnis der Sprache. Heidelberg: Quelle & Meyer, 1954.
- Okulicz, Jerzy (1986). Einige Aspekte der Ethnogenese der Balten und Slawen im Lichte archäologischer und sprachwissenschaftlicher Forschungen. Quaestiones medii aevi, Vol. 3, p. 7-34.
- Pokorny, Julius (1959). Indogermanisches Etymologisches Wörterbuch. Bern, München : Francke, 1959.
- Parczewski, Michał (1993). Die Anfänge der frühslawischen Kultur in Polen. Wien: Österreichische Gesellschaft für Ur- und Frühgeschichte, 1993. Veröffentlichungen der österreichischen Gesellschaft für Ur- und Frühgeschichte; Bd. 17.
- Pleterski, Andrej (1995). Model etnogeneze Slovanov na osnovi nekaterih novejših raziskav / A model of an Ethnogenesis of Slavs based on Some Recent Research. Zgodovinski časopis = Historical Review 49, No. 4, 1995, p. 537-556. ISSN 0350-5774. English summary: COBISS 4601165
- Schenker, Alexander M. (1996). The Dawn of Slavic: an Introduction to Slavic Philology. New Haven: Yale University Press, 1996. ISBN 0-300-05846-2.
- Skrbiš, Zlatko (2002). The Emotional Historiography of Venetologists: Slovene Diaspora, Memory and Nationalism. Focaal: European Journal of Anthropology 39, 2002, p. 41-56. 
- Steinacher, Roland (2002). Studien zur vandalischen Geschichte. Die Gleichsetzung der Ethnonyme Wenden, Slawen und Vandalen vom Mittelalter bis ins 18. Jahrhundert(doctoral thesis). Wien, 2002.
- Steinacher, Roland (2004). Wenden, Slawen, Vandalen. Eine frühmittelalterliche pseudologische Gleichsetzung und ihr Nachleben bis ins 18. Jahrhundert. In: W. Pohl (Hrsg.): Auf der Suche nach den Ursprüngen. Von der Bedeutung des frühen Mittelalters (Forschungen zur Geschichte des Mittelalters 8), Wien 2004, p. 329-353.
- Svašek, Maruška. Postsocialism politics and emotions in Central and Eastern Europe, Berghahn Books, 2006, ISBN 1-84545-124-4