Whenever I'm confronted with a situation like this - my first go-to response is to start documenting as much as I can. If the code is properly commented you may

Whenever I'm confronted with a situation like this - my first go-to response is to start documenting as much as I can. If the code is properly commented you may be able to use a tool like Doxygen to spit out some HTML documentation, which at least gives you a starting point to talk to people about the codebase. Generally speaking: 1) Stick to bug-fixing for a good few weeks / months. This is invaluable for figuring out the mess and understanding why it is the way it is. 2) Ask questions - don't be afraid of asking basic questions if you think something looks silly. More often than not there's a reason. 3) Improve the code in small chunks, but be mindful that what you consider an improvement may not be. 4) Understand that working as a team means you will need to accommodate varying levels of skill. 5) Don't blame individuals for bad code. Leave that to your superiors.