The dark triad is a group of three personality traits: narcissism, Machiavellianism and psychopathy. The use of the term "dark" reflects the perception that these traits have interpersonally aversive qualities:
- Narcissism is characterised by grandiosity, pride, egotism, and a lack of empathy.
- Machiavellianism is characterised by manipulation and exploitation of others; a cynical disregard for morality, and a focus on self-interest and deception.
- Psychopathy is characterised by enduring antisocial behaviour, impulsivity, selfishness, callousness, and remorselessness.
All three traits have been associated with a callous-manipulative interpersonal style. Jakobwitz and Egan carried out a factor analysis and found agreeableness strongly dissociated with these traits, and other factors, such as neuroticism and a lack of conscientiousness, associated with some traits. However, it has been suggested that agreeableness is not relevant to the core of the dark triad, and that instead the common variance is accounted for by callousness and manipulation.
Research on each of the traits represented in the dark triad began in isolation from one another. The term "Machiavellianism" dates back to the 16th century, and "narcissism" and "psychopathy" to the 19th century.
In 1998, McHoskey, Worzel, and Szyarto claimed that Machiavellianism is nothing more than a mild form of psychopathy: aside from their relative severity, there is no difference between them. Delroy L. Paulhus and McHoskey debated these perspectives at a subsequent American Psychological Association (APA) conference, inspiring research by Paulhus and Kevin M. Williams on the dark triad. Paulhus and Williams found enough behavioural, personality, and cognitive differences between the traits to suggest that they were different from each other; however, they concluded that further research was needed to elucidate how and why they overlap.
Subclinical dimensions vs. disorders
Two dark triad traits, narcissism and psychopathy, were initially proposed as explanations for observed clinical disorders. Narcissism was discussed in the writings of Sigmund Freud, and psychopathy as a clinical diagnosis was addressed in the early writings of Hervey Cleckley in 1941 with the publication of The Mask of Sanity. Given the dimensional model of narcissism and psychopathy, complemented by self-report assessments that are appropriate for the general population, these traits can now be studied at the subclinical level.
With respect to empirical research, psychopathy was not formally studied until the 1960s and 1970s with the pioneering efforts of Robert Hare, in his Psychopathy Checklist (PCL) and its revision (PCL-R). Hare notes in his book, "Without Conscience"  that asking psychopaths to self-report on psychologically important matters does not necessarily provide accurate or unbiased data. However, recent efforts have been made to study psychopathy in the dimensional realm using self-reported instruments, as with the Levenson Primary and Secondary Psychopathy Scales, The Psychopathic Personality Inventory, and the Self-Report Psychopathy Scale.
Similarly, narcissism lacked a means of assessing the disorder outside of clinical interviews, until the popular "Narcissistic Personality Inventory" was created by Raskin and Hall in 1979. Since the NPI, several other measures have emerged which attempt to provide self-report alternatives for personality disorder assessment. In addition, new instruments have been developed to study "pathological" narcissism  as opposed to "grandiose" narcissism, which is what many argue the NPI measures.
Machiavellianism has never been referenced in any version of the Diagnostic and Statistical Manual (DSM) for psychological disorders. It has been treated as strictly a personality construct. The original published versions of the Mach-IV and Mach-V scales  are still the most widely used in empirical research.
As a disorder
In general, researchers treat these traits as pathological, something that needs to be treated, and inherently undesirable, e.g. socially condemned or personally counter-productive. However, some argue that this view of the traits is the result of researchers having an implicit group selection orientation towards personality traits.
In the workplace
Two studies published in 2013 and 2014 have found that people who are identified as trolls tend to have dark personality traits and show signs of sadism, antisocial behavior, psychopathy, and Machiavellianism. The 2013 study suggested that there are a number of similarities between anti-social and flame trolling activities and the 2014 study suggested that the noxious personality characteristics known as the "dark triad of personality" should be investigated in the analysis of trolling, and concluded that trolling appears "to be an Internet manifestation of everyday sadism." Their relevance is suggested by research linking these traits to bullying in both adolescents and adults.
As mating strategy
It has been suggested that the dark triad traits appear to predispose individuals to short-term rewards and relationships over long-term rewards and benefits. Although advanced societies attempt to promote long-term thinking (environmental protection, saving money for retirement), there are reproductive benefits for the individual for thinking and acting on a shorter time-course. 
Consistent with this perspective, studies have suggested that on average, those who exhibit the dark triad of personality traits have an accelerated mating strategy, reporting more sex partners, more favorable attitudes towards casual sex, lowered standards in their short-term mates, a tendency to steal or poach mates from others, more risk-taking in the form of substance abuse, a tendency to prefer immediate but smaller amounts of money over delayed but larger amounts of money, limited self-control and greater incidence of ADHD symptoms and a pragmatic and game-playing love style. These traits have been identified as part of a fast life strategy that appears to be enacted by an exploitative, opportunistic, and protean approach to life in general and at work.
Contrarily, there is a lack of empirical evidence for a correlation between psychopathy and reproductive success. Additionally, using established measures of the dark triad, these traits are not universally short-term-oriented nor are they all impulsive. Furthermore, much of the research reported pertaining to the dark triad cited in the above paragraph is based on statistical procedures that erroneously assume the dark triad are a single construct, in spite of genetic and meta-analytic evidence to the contrary.
Vulnerable dark triad
The "vulnerable dark triad" (VDT) is composed of three related and similar constructs: vulnerable narcissism, factor 2 psychopathy, and borderline personality disorder. A study found that vulnerable narcissism, factor 2 psychopathy, and borderline personality disorder are significantly related to one another and manifest similar nomological networks. Although the VDT members are related to negative emotionality and antagonistic interpersonal styles, they are also related to introversion and disinhibition.
- Robert M. Regoli; John D. Hewitt; Matt DeLisi (20 April 2011). Delinquency in Society: The Essentials. Jones & Bartlett Learning. p. 99. ISBN 978-0-7637-7790-6.
- W. Keith Campbell; Joshua D. Miller (7 July 2011). The Handbook of Narcissism and Narcissistic Personality Disorder: Theoretical Approaches, Empirical Findings, and Treatments. John Wiley & Sons. p. 154. ISBN 978-1-118-02924-4.
- Mark R. Leary; Rick H. Hoyle (5 June 2009). Handbook of individual differences in social behavior. Guilford Press. p. 100. ISBN 978-1-59385-647-2.
- Tomas Chamorro-Premuzic; Sophie von Stumm; Adrian Furnham (23 February 2011). The Wiley-Blackwell Handbook of Individual Differences. John Wiley & Sons. p. 527. ISBN 978-1-4443-4310-6.
- Paulhus, D. L., Williams, K. M. (2002). "The Dark Triad of personality: narcissism, Machiavellianism, and psychopathy". Journal of Research in Personality 36 (6): 556–63. doi:10.1016/S0092-6566(02)00505-6.
- Leonard M. Horowitz; Stephen Strack, Ph.D. (14 October 2010). Handbook of Interpersonal Psychology: Theory, Research, Assessment and Therapeutic Interventions. John Wiley & Sons. pp. 252–55. ISBN 978-0-470-88103-3. Retrieved 15 February 2012.
- David Lacey (17 March 2009). Managing the Human Factor in Information Security: How to Win Over Staff and Influence Business Managers. John Wiley & Sons. p. 248. ISBN 978-0-470-72199-5.
- Kohut, H. (1977). The Restoration of the Self. New York: International Universities Press.
- Jakobwitz, S., Egan, V. (2006). "The 'dark triad' and normal personality traits". Personality and Individual Differences 40 (2): 331–39. doi:10.1016/j.paid.2005.07.006.
- Skeem, J. L.; Polaschek, D. L. L.; Patrick, C. J.; Lilienfeld, S. O. (2011). "Psychopathic Personality: Bridging the Gap Between Scientific Evidence and Public Policy". Psychological Science in the Public Interest 12 (3): 95–162. doi:10.1177/1529100611426706.
- Jones, D. N., Paulhus, D. L. (2010). "Differentiating the Dark Triad within the interpersonal circumplex". In Horowitz, L. M., Strack, S. N. Handbook of interpersonal theory and research. New York: Guilford. pp. 249–67.
- Jones, D. N., & Figueredo, A. J. (in press). "The core of darkness: Uncovering the heart of the Dark Triad". European Journal of Personality.
- Berrios, G.E. (1999). "Classic Text No. 37: J. C. Prichard and the concept of 'moral insanity'". History of Psychiatry 10 (37): 111–26. doi:10.1177/0957154X9901003706. PMID 11623816.
- Berrios, G.E. (1993). "European views on personality disorders: A conceptual history". Comprehensive Psychiatry 34 (1): 14–30. doi:10.1016/0010-440X(93)90031-X. PMID 8425387.
- McHoskey J. W., Worzel W., Szyarto C. (1998). "Machiavellianism and psychopathy". Journal of Personality and Social Psychology 74 (1): 192–210. doi:10.1037/0022-35188.8.131.52. PMID 9457782.
- Cleckly, H. C. (1941). The Mask of Sanity: An Attempt to Reinterpret the So-Called Psychopathic Personality. St. Louis, MO: Mosby.
- LeBreton, J. M., Binning, J. F., & Adorno, A. J. (2005). Sub-clinical psychopaths. In D. L. Segal & J. C. Thomas (Eds.), Comprehensive handbook of personality and psychopathology: Vol. 1. Personality and everyday functioning (pp. 388–411). New York: John Wiley.
- Hare, R.D., (1991). The Hare Psychopathy Checklist-Revised. Toronto: Multi-Health Systems.
- Hare, R. D. (1999). Without conscience: The disturbing world of the psychopaths among us. New York: Guilford Press.
- Levenson M. R., Kiehl K. A., Fitzpatrick C. M. (1995). "Assessing psychopathic attributes in a noninstitutionalized population". Journal of Personality and Social Psychology 68 (1): 151–58. doi:10.1037/0022-35184.108.40.206. PMID 7861311.
- Lilienfeld S. O., Andrews B. P. (1996). "Development and preliminary validation of a self-report measure of psychopathic personality traits in noncrimnal population". Journal of Personality Assessment 66 (3): 488–524. doi:10.1207/s15327752jpa6603_3. PMID 8667144.
- Paulhus, D. L., Neumann, C. S., & Hare, R. D. (in press). Manual for the Self-Report Psychopathy scale (SRP). Toronto, ON: Multi-Health Systems.
- Raskin R., Hall C. S. (1979). "A Narcissistic Personality Inventory". Psychological Reports 45 (2): 590. doi:10.2466/pr0.19220.127.116.110.
- Hyler, S.E. (1994). Personality Diagnostic Questionnaire-4 (Unpublished test). New York: NYSPI.
- Pincus A. L., Ansell E. B., Pimentel C. A., Cain N. M., Wright A. G. C., Levy K. N. (2009). "Initial construction and validation of the Pathological Narcissism Inventory". Psychological Assessment 21 (3): 365–79. doi:10.1037/a0016530. PMID 19719348.
- Miller, J. D., & Campbell, W. K. (2008). Comparing clinical and Social-Personality Conceputalizations of narcissism. Journal of Personality, 76, 449–476.
- Wink P (1991). "Two faces of narcissism". Journal of Personality and Social Psychology 61 (4): 590–97. doi:10.1037/0022-3518.104.22.1680. PMID 1960651.
- Christie, R., & Geis, F. L. (1970). Studies in Machiavellianism. New York: Academic Press.
- Jones, D. N., & Paulhus, D. L. (2009). Machiavellianism. In M. R. Leary & R. H. Hoyle (Eds.), Handbook of Individual Differences in Social Behavior (pp. 93–108). New York: Guilford.
- Jones D.N., Paulhus D. L. (2010). "Different provocations trigger aggression in narcissists and psychopaths". Social Psychological and Personality Science 1: 12–18. doi:10.1177/1948550609347591.
- Hodson, G. M., Hogg, S. M., & MacInnis, C. C. (2009). The role of "dark personalities" (narcissism, Machiavellianism, psychopathy), Big Five personality factors, and ideology in explaining prejudice. Journal of Research in Personality, 43, 686–690.
- Chabrol H., Van Leeuwen N., Rodgers R., Séjourné S. (2009). "Contributions of psychopathic, narcissistic, Machiavellian, and sadistic personality traits to juvenile delinquency". Personality and Individual Differences 47 (7): 734–39. doi:10.1016/j.paid.2009.06.020.
- James O Office Politics: How to Thrive in a World of Lying, Backstabbing and Dirty Tricks (2013)
- Buckels, Erin E.; Trapnell, Paul D.; Paulhus, Delroy L. (2014). "Trolls Just Want to Have Fun". Elsevier Ltd. Retrieved 2014-02-20.
- Bishop, Jonathan (2013). "The effect of de-individuation of the Internet Troller on Criminal Procedure implementation: An interview with a Hater". International Journal of Cyber Criminology 7 (1). pp. 28–48.
- Jonason P. K., Li N. P., Webster G. W., Schmitt D. P. (2009). "The Dark Triad: Facilitating short-term mating in men". European Journal of Personality 23: 5–18. doi:10.1002/per.698.
- Jonason P. K., Valentine K. A., Li N. P., Harbeson C. L. (2011). "Mate-selection and the Dark Triad: Facilitating a short-term mating strategy and creating a volatile environment". Personality and Individual Differences 51 (6): 759–63. doi:10.1016/j.paid.2011.06.025.
- Jonason P. K., Li N. P., Buss D. M. (2010). "The costs and benefits of the Dark Triad: Implications for mate poaching and mate retention tactics". Personality and Individual Differences 48 (4): 373–78. doi:10.1016/j.paid.2009.11.003.
- Jonason P. K., Koenig B., Tost J. (2010). "Living a fast life: The Dark Triad and Life History Theory". Human Nature 21 (4): 428–42. doi:10.1007/s12110-010-9102-4.
- Jonason, P. K., Li N. P., & Teicher, E. A. (2010). Who is James Bond?:The Dark Triad as an agentic social style. Individual Differences Research, 8, 111–120.
- Jonason, P. K., & Tost, J. (2010). I just cannot control myself: The Dark Triad and self-control. Personality and Individual Differences, 49, 611–615.
- Jonason, P.K., & Kavanagh, P. (2010). The dark side of love: The Dark Triad and love styles. Personality and Individual Differences, 49, 606–610.
- Jonason P.K., Webster G.D. (2012). "A protean approach to social influence: Dark Triad Personalities and Social Influence Tactics". Personality and Individual Differences 52 (4): 521–26. doi:10.1016/j.paid.2011.11.023.
- Jonason P. K., Slomski S., Partyka J. (2012). "The Dark Triad at work: How toxic employees get their way". Personality and Individual Differences 52 (3): 449–53. doi:10.1016/j.paid.2011.11.008.
- Jonason, P. K. & Tost, J. (2010). I just cannot control myself: The Dark Triad and self-control. Personality and Individual Differences, 49, 611–615.
- Jones D. N., Paulhus D. L. (2011). "The role of impulsivity in the Dark Triad of personality". Personality and Individual Differences 51 (5): 679–82. doi:10.1016/j.paid.2011.04.011.
- Vernon P. A., Villani V. C., Vickers L. C., Harris J. A. (2008). "A behavioral genetic investigation of the Dark Triad and the Big Five". Personality and Individual Differences 44 (2): 445–52. doi:10.1016/j.paid.2007.09.007.
- O'Boyle E. H., Forsyth D. R., Banks G. C., McDaniel M. A. (2012). "A meta-analysis of the Dark Triad and work behavior: A social exchange perspective". Journal of Applied Psychology 97 (3): 557–79. doi:10.1037/a0025679. PMID 22023075.
- Chabrol H., Van Leeuwen, N., Rodgers, R., & Sejourne, N. (2009). Contributions of psychopathic, narcissistic, Machiavellian, and sadistic personality traits to juvenile delinquency. Personality and Individual Differences, 47(7), 734–739.
- Buckels, E. E.; Jones, D. N.; Paulhus, D. L. (2013). "Behavioral confirmation of everyday sadism". Psychological Science. doi:10.1177/0956797613490749.
- Miller, JD.; Dir, A.; Gentile, B.; Wilson, L.; Pryor, LR.; Campbell, K. (October 2010). "Searching for a Vulnerable Dark Triad: Comparing Factor 2 Psychopathy, Vulnerable Narcissism, and Borderline Personality Disorder". Journal of Personality 78 (5): 1529–1564. doi:10.1111/j.1467-6494.2010.00660.x.
- Peter K. Jonason and Gregory D. Webster have published a brief measure of the dark triad traits called "The Dirty Dozen".
- Daniel N. Jones and Delroy L. Paulhus have also created a brief measure of the dark triad called the SD3 or Short Dark Triad, which can be found here.
- Mooney, Chris (February 14, 2014). "Internet Trolls Really Are Horrible People: Narcissistic, Machiavellian, psychopathic, and sadistic". Slate.