What type of Fonts are compatible between Mac and PC?

Hello all:
I work in InDesign primarily from a Windows based PC. I occasionally do some work on a Mac as well. I have a mixture of font type I use (TTF, OpenType etc) on my PC. I know a lot of font types are not compatible between PC and Mac. My questions is, are OpenType fonts compatible with Mac?

What suggestions would you give to people working on two platforms as to how to best manage their font library (short of buying two versions of the same fonts)?

Thanks.