In a nutshell. The CPL/IR or ATPL exams (depending on the direction you want to go), prescribed training and flight tests for CPL and IR.
The reference you are looking for is in JAR FCL1 under licence conversion. If you look in the appendix it will give you the experience credits as well.
If you are looking to do it in the UK the LASORS is a handy guide but is full of errors and is not the actual regulation (just our CAA interpretation)which is currently JAR FCL and will be EASA Part FCL from April next year.