Horsemanship is a keyword ability on creatures that serves as an evasion ability. Attacking creatures with horsemanship can not be blocked by creatures without horsemanship. It is functionally identical to flying. However, horsemanship is considered parasitic (meaning that it only interacts with other things in the set rather than the rest of Magic). 
All cards with horsemanship appear in Portal Three Kingdoms. Until the set was made legal for Vintage and Legacy in October 2005, it had the distinction of being the only keyword ability existing outside of Un-sets that did not appear on a single card legal in any tournament format.
- Horsemanship doesn't interact with flying or reach.
- If a creature gains or loses horsemanship after blockers have been declared, it won't cause those blocks to change.
Cards that grant Horsemanship