What is the maximum number of projects allowed on an engagement? There really is no limit, although in practicality there are some things to consider.

If the engagement has long running projects you may run into performance problems on individual projects. See How do I set up ongoing non-billable projects
Clicking through 100 projects to get to the one you want could be annoying
Resources may end up with very large timesheets

If possible, it may make sense to try and leverage fewer projects with more Task Types.

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