When people do things with words, how do we know what they are doing? Many scholars have assumed a category of things called actions: 'requests', 'proposals', 'complaints', 'excuses'. The idea is both convenient and intuitive, but as this book argues, it is a spurious concept of action. In interaction, a person's primary task is to decide how to respond, not to label what someone just did. The labeling of actions is a meta-level process, appropriate only when we wish to draw attention to others' behaviors in order to quiz, sanction, praise, blame, or otherwise hold them to account. This book develops a new account of action grounded in certain fundamental ideas about the nature of human sociality: that social conduct is naturally interpreted as purposeful; that human behavior is shaped under a tyranny of social accountability; and that language is our central resource for social action and reaction.