Audit logging, for example, the history of changes done to your users (for eg: who updated, edited, or disabled a given user), is available in FogBugz but is not enabled by default.
We currently do not offer audit logging for On-Demand customers, since it is not a request we get too often from our On-Demand customers. If you need this feature for your On-Demand account, please contact us. We will evaluate your request, and come back to you with a proposal.
Audit logging for On-Premises customers can be configured as per the logging configuration guide. This guide also lists what actions are logged as audit log events, and what information is logged about these events.
Plan ahead for the required disk space and performance impact.