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The term first-generation can refer to either people who were born in one country and relocated to another at a young age, or to their children born in the country they have relocated to. The term second-generation refers to children of first-generation immigrants, and thus exhibits the same ambiguity. The term 1.5 generation is a term coined for people who identify as "first generation" yet, lack the necessary acculturation.
The term first-generation, as it pertains to a person's nationality or residency in a country, can imply two possible meanings, depending on context:
- A native-born citizen or resident of a country whose parents are foreign born: e.g., "first-generation" American,
- A foreign born citizen or resident who has immigrated to a new country of residence: e.g., "first-generation" migrant, thus second-generation American.
- ...designating a member of the first (or second, etc.) generation of a family to do something or live somewhere; spec. designating a naturalized immigrant or a descendant of immigrant parents, esp. in the United States.... (OED definition of "generation," section 6b., emphasis added)b
In the United States, among demographers and other social scientists, the term "first generation" is used to refer to foreign-born residents (excluding those born abroad of American parents).
There is no universal consensus on which of these meanings is always intended.
The term 1.5 generation or 1.5G refers to two types of people. Individuals who immigrate to a new country before or during their early teens (Asher 2011). They earn the label the "1.5 generation" because they bring with them or maintain characteristics from their home country, meanwhile engaging in assimilation and socialization with their new country. Often times, in the case of small children, a battle of linguistic comprehension occurs between their academic language and the language spoken at home (Asher 2011). Their identity is thus, a combination of new and old culture and tradition. Sociologist Ruben Rumbaut was among the first to use the term to examine outcomes among those arriving in the United States before adolescence, but since then the term has expanded to include foreign students, as well as other unique individuals. 
Depending on the age of immigration, the community where they settle, extent of education in their native country, and other factors, 1.5 generation individuals identify with their countries of origin to varying degrees. However, their identification is affected by their experiences growing up in the new country. 1.5G individuals are often bilingual and find it easier to assimilate into local culture and society than people who immigrate as adults. Many 1.5 generation individuals also, become bi-cultural, combining both cultures - culture from the country of origin with the culture of the new country.
The term "second-generation" extends the concept of first-generation by one generation. As such, the term exhibits the same type of ambiguity as "first-generation," as well as additional ones.
Like "first-generation immigrant," the term "second-generation" can refer to a member of either:
- The second generation of a family to inhabit, but the first natively born in, a country, or
- The second generation born in a country
The term second-generation immigrant attracts criticism due to it being an oxymoron. Namely, critics say, a "second-generation immigrant" is not an immigrant, since being "second-generation" means that the person is born in the country and the person's parents are the immigrants in question. Generation labeling immigrants is further complicated by the fact that immigrant generations may not correspond to the genealogical generations of a family. For instance, if a family of two parents and their two adult children immigrate to a new country, members in both generations of this family may be considered "first generation" by the former definition, as both parents and children were foreign-born, adult, immigrants. Likewise, if the two parents had a third child later on, this child would be of a different immigrant generation from that of its siblings. For every generation, the factor of mixed-generation marriages further convolutes the issue, as a person may have immigrants at several different levels of his or her ancestry.
These ambiguities notwithstanding, generation labeling is frequently used in parlance, news articles , and reference articles without deliberate clarification of birthplace or naturalization. It may or may not be possible to determine, from context, which meaning is intended.
When demographers and other social scientists in the United States use the term "second generation," they usually refer to people with one foreign-born parent. Some researchers have begun to question whether those with one native-born parent and those with no native-born parents should be lumped together, with evidence suggesting that there are significant differences in outcomes between the two groups.
1.75 and 1.25 generations
Rubén G. Rumbaut has coined the terminology "1.75 generation" and "1.25 generation" immigrants, for children who are closer to birth or full adulthood when they immigrate. Children who arrive in their early childhood (ages 0 to 5) are referred to as 1.75 generation immigrants since their experiences are closer to a true 2nd-generation immigrant who was born in the Country they live in: they retain virtually no memory of their country of birth, were too young to go to school to learn to read or write in the parental language in the home country, typically learn the language of the Country they immigrate to without an accent and are almost entirely socialized there. Children who arrive in their adolescent years (ages 13-17) are referred to as 1.25 generation immigrants because their experiences are closer to the first generation of immigrants adults than to the native born second generation.
In the United States
- First generation immigrant: immigrant who migrated to the U.S.
- Second generation immigrant: U.S.-born children of at least one foreign-born parent.
- Third generation: U.S.-born children of at least one U.S.-born parent, where at least one grandparent is foreign-born.
- Inequality within immigrant families in the United States
- Second-generation immigrants in the United States
- Cultural assimilation
- "Nation's Foreign-Born Population Nears 37 Million". Press Release. U.S. Census Bureau. Retrieved 31 January 2012.
- Rojas, Leslie Berenstein. "Introducing the cultural mashup dictionary: Our first term, 1.5 generation". Article. Southern California Public Radio. Retrieved 31 January 2012.
- Ramakrishnan, S. Karthick (2004). "Second‐Generation Immigrants? The "2.5 Generation" in the United States". Social Science Quarterly. 85 (2): 380–399. doi:10.1111/j.0038-4941.2004.08502013.x. Retrieved 31 January 2012.
- Acevedo-Garcia, Dolores; Jocelyn Pan; Hee-Jin Jun; Theresa L. Osypuk; Karen M. Emmons (2005). "The effect of immigrant generation on smoking". Social Science & Medicine. 61 (6): 1223–1242. doi:10.1016/j.socscimed.2005.01.027. Retrieved 31 January 2012.
- Rumbaut, Rubén. Ages, Life Stages, and Generational Cohorts: Decomposing the Immigrant First and Second Generations in the United States. p. 1167’’ http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1887924 Retrieved December 9, 2014.
- "generation, n.". OED Online. December 2011. Oxford University Press. 9 January 2012 <>.
- McLellan, Janet. (1999). Many Petals of the Lotus: Five Asian Buddhist Communities in Toronto. Toronto: University of Toronto Press. ISBN 9780802044211; ISBN 9780802082251; OCLC 247672282
- Asher, C. (2011). The progressive past: How history can help us serve generation 1.5. Reference & User Service Quarterly , 51(1). 43-48.
- Amaya, Ismael. (2010). "How First-Generation College and Underrepresented Students Can Overcome Obstacles to Attaining a College Education: Handbook for a New Family Tradition,"Paper 318. Applied Research Projects. Texas State University.