Summary: This paper discusses the role of emotions in artificial agent design and implementation. The syntax and semantics of a simplified version of a logic-based agent-oriented programming language is presented. This programming language facilitates the implementation of artificial agents with emotions. Four types of emotions are distinguished: happiness, sadness, anger, and fear. These emotions are defined relative to agent's goals and plans. The emotions result from the agent's deliberation process and influence the deliberation process. The semantics of each emotion type is incorporated in the transition semantics of the presented agent-oriented programming language.