Challenges express the speaker's intention not to comply with a proposition, force or presupposition communicated in and through a prior conversational contribution. This may be a directly adjacent contribution, some less directly adjacent contribution, or a conversational contribution uttered in some prior discourse. As for its sequential status, a challenge is a responsive contribution, and from an interpersonal perspective, it tends to carry a high degree of face-threatening potential. A felicitous analysis of a challenge thus needs to go beyond a single conversational contribution, not only accommodating context but also the nature of a challenge's embeddedness in context. The contribution is organized as follows: The first section systematizes the necessary and sufficient contextual constraints and requirements for a conversational contribution to be assigned the status of a challenge. The second part argues for a challenge to be conceptualized as a particularized contextual configuration, which may serve as a tertium comparationis in contrastive pragmatics. The third section exemplifies the frame of reference with a contrastive analysis of British and German challenges adopted from a corpus of political interviews. In both sets of data, challenges tend to be realized implicitly, and in both sets, challenging the content of a contribution is more frequent than challenging its force or presuppositions. While the British data display a wider variety of challenges, the German data prefer the content-based, implicitly realized challenge.