During the annual meetings of baseball every winter there is a short reorganization of baseball teams. It's called the Rule 5 draft.
During this draft a certain group of players from each team are protected and a certain group of players can be selected by the rest of the teams.
I know that specifically players that have been recently drafted, and players on the 40 man roster are not eligible to be taken in the Rule 5 draft.
What I'm unclear on is when a player becomes eligible for the draft, and how he might be protected in addition to lack of service time and being added to the 40 man roster.
What are the eligibility criteria to be selected in the rule 5 drift and what ways are there to protect a player outside of the 40 man roster?