The Oxford Research Encyclopedia of Criminology and Criminal Justice is an excellent resource if you're looking to gain insight into a particular topic. It's possible to either search or browse the encyclopedia. Broad subject areas are outlined below:
Each entry provides a detailed discussion of the subject matter, and includes suggestions for further reading, and a reference list. New entries are regularly being added to the encyclopedia, and so it will continue to grow in scope.
Highly recommended for criminology students.