Our own experience in developing agents and multi-agent systems painfully taught us that there are no instruments to support the implementation of such systems. A thorough literature study confirms the fact that implementation issues, which are definitely non-trivial but clearly underestimated, are mostly achieved in an ad hoc fashion. This obviously results in people reinventing solutions for common problems. In this paper, we propose agent implementation patterns as an instrument to describe problems and generic solutions for implementing agents and multi-agent systems. Agent implementation patterns contrast with other proposals of agent patterns in that the latter typically deal with architectural and conceptual models, and not with the actual implementation of agent characteristics. If we eventually want to come to a best practice for the development and implementation of agent systems, system developers should share their knowledge and experience gained during the implementation of their systems. Agent implementation patterns can contribute to formalize and share such knowledge.