In conversation, an important part of the information conveyed is not explicitly said but implicated. Implicatures are an extremely broad phenomena, which can involve different contextual elements and types of inference. In this book I investigate implicatures that arise from causal dependencies between actions, such as the following. Mary told Bill ''The chest is locked. The crown is inside.'' Bill replied ''Give me the crown.'' With his utterance, Bill implicated that Mary had to open the chest. Conversation provides an intrinsic mechanism for carrying out negotiations of meaning, namely clarifications. Mary could coherently continue the conversation with the clarification request ''How can I open the chest?'', making the implicature explicit. Exploring clarifications requests in dialogue, I present empirical evidence, from human-human dialogue corpora, which shows what kinds of implicatures are inferred and processed by dialogue participants in a task-oriented dialogue. Moreover, I discuss the design and implementation of a text-adventure game, that is able to synthesize and negotiate conversational implicatures in the interactive fashion observed in the empirical study.