Why is it that a small proportion of the population accounts for the majority of crime? This question has stimulated a great deal of theoretical and methodological controversy in criminology. In essence, the debate is rooted in different theoretical underpinnings of continuity and change in crime, and the extent to which it is possible to foresee a life of crime by zeroing in on at-risk juvenile offenders. The current thesis explores four contentious empirical issues that may move this debate forward: the long-term predictability of persistent offending in adulthood on the basis of childhood risk factors (Study I); the magnitude of adult-onset offending (Study II); the predictive value of gender for criminal recidivism (Study III); and the association between birth cohort membership and criminal career parameters (Study IV). All four studies employ longitudinal Swedish administrative data, based on cohorts of individuals born between the early 1940s and the mid-1980s, and followed on the basis of detailed conviction data. The thesis also utilizes qualitative life-history narratives with former at-risk juvenile delinquents. The results suggest that theories aiming to explain crime beyond the transition to adulthood should incorporate factors presumed to cause within-individual change, even among high-risk juvenile offenders. Although childhood cumulative risk, including a wide range of individual, family, school, and peer measures, were clearly associated with adult crime, they had limited value for predicting those persistent offenders who eventually ended up in the tail of the crime distribution. Furthermore, although gender is generally one of the main demographic predictors of criminal convictions, the results indicate that it is important to include females for the purpose of understanding continuity and change in adulthood. This is in part because adult-onset offending is more prevalent within the female offending population than within the male offending population and in part because the risk for criminal recidivism among female offenders becomes increasingly similar to that found among male offenders as convictions accumulate over the life span. Finally, the results suggest that the typical criminal career has undergone significant changes both within and across gender groups during the period since the mid-1970s, a period which has witnessed a historical decline in the aggregate conviction rate in Sweden. Taking this into consideration, the employment and extensive analysis of longitudinal multiple cohort data ought to provide a basis for furthering our knowledge on the inherent complexity of crime trends, while at the same time also locating the study of criminal careers in its historical context.