This paper aims to propose that Problem-Based Learning (PBL) is a method that can help meet the conditions in language learning and instruction. PBL was first used in medical education, where learners engaged in problem-solving activities that reflect the demands of real-life professional practice, thus promoting critical thinking in the content domain. The paper proposes that by applying PBL in language learning and creating situations in which learners work collaboratively on problems, the learners benefit in two respects: (i) they have the opportunity to practise the kind of thinking skills and problem-solving strategies needed in real life, and (ii) they engage in purposeful language activity with others through discussion and negotiation. The paper first provides a theoretical rationale far the use of PBL in language learning and suggests attendant changes in the role of a language instructor in a PBL context. The paper then presents an outline of the stages and components needed in designing an online PBL Unit far use in an undergraduate language class.