More precisely referred to as "action drafting", this mechanism requires players to select individual actions from a set of actions available to all players. Players generally select actions one-at-a-time and in turn order. There is usually(*) a limit on the number of times a single action may be taken. Once that limit for an action is reached, it typically either becomes more expensive to take again or can no longer be taken for the remainder of the round. As such, not all actions can be taken by all players in a given round, and action "blocking" occurs. If the game is structured in rounds, then all actions are usually refreshed at the start or end of each round so that they become available again.
Actions are commonly selected by the placement of game pieces or tokens on the selected actions. Each player usually has a limited number of pieces with which to participate in the process. Some games achieve the same effect in reverse: the turn begins with action spaces filled by markers, which are claimed by players for some cost.
From a thematic standpoint, the game pieces which players use to draft actions often represent workers of a given trade (this category of mechanism, however, is not necessarily limited to or by this thematic representation). In other words, players often thematically "place workers" to show which actions have been drafted by individual players. For example, in Agricola each player starts with two pieces representing family members that can be placed on action spaces to collect resources or take other actions like building fences. When someone places a piece on a given space, that action is no longer available until the next round.
Keydom, which was published in 1998, is widely recognized as the first of the worker placement genre of games. Early design experiments with the mechanism include Way Out West (2000) and Bus (1999). Well known examples of worker placement include Agricola (2007), Caylus (2005) and Stone Age (2008).
(*)The use of the word "usually" in this context is a somewhat controversial point of discussion. There are many who feel that 'action blocking' is a defining element of worker placement. In that case, there must always be a limit on the number of times a single action may be drafted each round.
Currently, the oldest dated and tagged game is Silverton (1991), although the included tag is controversial since the mechanisms do not meet many of the accepted criteria noted above.
Worker Placement fan
Worker Placement fan