When speakers produce “I don't knows” in ordinary conversation, they claim insufficient knowledge about the matters at hand. Analysis of diverse conversational environments reveal, however, that speakers’claims nevertheless accomplish a variety of subtle actions. “I don't knows” may be strategically and ambiguously deployed across the following achievements: (a) marking uncertainty and concerns about next-positioned opinions, assessments, or troubles; (b) constructing neutral positions, designed to mitigate agreement and disagreement, by disattending and seeking closure on other-initiated topics (e.g., moving toward completing stories or working to avoid troubling issues); and (c) postponing or withholding acceptance of others’invited and requested actions. By examining moments where insufficient knowledge claims are contingently used as a resource, understandings of proactive yet delicately managed interactional conduct are forwarded. Such conduct is shown to be anchored in ordinary conversations but adapted in similar yet distinct ways within institutional interactions such as courtroom cross-examination.