Quark Matter 99 --- Theoretical Summary: What Next?

I review the three broad areas where major progress has been reported: The phase structure of strongly interacting matter, the properties of matter at the instant when it freezes out into individual hadrons in the final stage of the expansion of the hot fireball, and the status of the main signatures of the formation of a quark-gluon plasma. In the final section I present some thoughts about what should be done next, both in the experiemntal and the theoretical arena.