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The domain of individual differences in 
youth has traditionally been studied by tem -
perament researchers. Temperament dif -
ferences  were generally defined as biologi -
cally based differences in formal aspects of 
behavior (Strelau & Zawadzki, 2012) that 
are observable early in development (Thom -
as, Chess, Birch, Herzig, & Korn, 1963) 
and show a substantial rank-order stability 
across time (Karevold, Mathiesen, Baardstu, 
& Sanson, 2018; Thomas & Chess, 1977). 
In contrast, the term personality  referred 
mainly to individual differences in behav -
iors, feelings, and cognitions in adulthood, 
resulting from the interaction between the 
formal characteristics of temperament with 
different environmental influences, crystal -
lized into personality traits. In this concep -
tualization, temperament traits are seen as 
a starting point of a series of developmental 
and interactive processes with the environ -
ment (Karevold et al., 2018) that ultimately 
form an individual’s personality, that is, how 
he or she perceives him- or herself (identity) 
or is perceived by others (reputation).
Nowadays, however, the terms tempera -
ment  and personality  are used more and more 
interchangeably (Shiner & Caspi, 2003). 
There is substantive evidence, for example, 
that personality traits are also observable early on in development and have biologi -
cal underpinnings, two defining features of 
temperament traits (De Fruyt & Van Leeu -
wen, 2014). At an operational level, items to 
assess temperament constructs are difficult 
to distinguish from those used to indicate 
personality traits. Finally, the dimensions 
put forward in models advancing a concep -
tual distinction between temperament traits 
on the one hand and character/personality 
traits on the other, such as Cloninger’s tem -
perament and character model (Cloninger, 
Svrakic, & Przybeck, 1993), were shown to 
have strong associations with the personal -
ity dimensions Neuroticism, Extraversion, 
Openness to Experience, Agreeableness and 
Conscientiousness of the five-  factor model 
(FFM; De Fruyt, Van de Wiele, & Van Heer -
ingen, 2000). Together, these multiple sourc -
es of evidence suggest that the concepts of 
temperament and personality have much in 
common, and are probably more alike than 
different, and that temperament is a subor -
dinated concept of personality.
These conceptual and empirical conver -
gences (Mervielde & Asendorpf, 2000) have 
been well established in the study of ado -
lescent individual differences, in which per -
sonality traits and personality development 
were studied in their own right, but also in CHAPTER 13
Personality in  Adolescence
Filip De Fruyt  
Evalill  Bølstad  Karevold