This article provides a theoretical and empirical argument in support of explicit language instruction. It proposes on theoretical grounds that certain features of a language are sufficiently complex and subtle that learners are unlikely to be able to decipher their full conceptual meaning on the basis of exposure alone. It further proposes that the kind of explicit instruction that has been assumed in much of SLA research - based on structural rules of thumb - is inappropriate and that an alternative approach, grounded in principles of sociocultural theory is an effective means of promoting development, which in the theory calls for both explicit conceptual knowledge and extensive and intensive communicative practice. The approach, or model, is referred to as Concept-based Language Instruction (C-BLI). Empirical support for explicit instruction using C-BLI is derived from pedagogical studies using the model. In addition, evidence from L2 neuroscience ERP research is considered as well as evidence from cultural evolution. The principles of C-BLI are compared to those supporting Dynamic Usage-Based instruction which emerges from L2 research informed by Complex Dynamic Systems Theory.