A sample of 698 English male prisoners who had each been convicted of at least two standard list offences was investigated. The probability of switching from one offence to another remained constant over successive convictions in agreement with Markov chain hypothesis. Contrary to the hypothesis, however, the past history of types of offences helped to predict future types of offences, suggesting that there was some specialization in offending. This was confirmed and quantified by the forward specialization coefficient. The most specialized offenders were sex offenders, and the most persistent offenders became increasingly specialized in fraud. When the extent to which one sentence followed another was studied, the stepping-stone nature of the sentencing tariff was revealed. 6 tables, 39 references. (Author abstract modified)