Theoretical approaches within the cognitive-interactionist framework (Long, 2015) have identified various aspects of L2 input and characteristics of instruction that predict learners’ L2 outcomes. Such strategies of L2 teaching relate to shaping characteristics of communicative activities in which the L2 is embedded and modifying L2 input, L2 interactions and learners’ L2 output. These strategies are in line with task-based and content-based teaching approaches. This article starts out with theoretical underpinnings to L2 instructional principles. It introduces the roles of sensory input and individual perception, internal knowledge construction, prior knowledge, and selective attention as understood within this framework. Consequences of this type of processing for instruction are discussed with respect to the instigation of noticing, salience, cognitive activation, learning from insight and depth of processing. The second part gives an overview of characteristics of teachers’ linguistic behaviour, which includes how teachers modify verbal and non-verbal L2 input, shape communicative activities and interactions in terms of authenticity, negotiation of meaning, feedback and focus on form, and create opportunities for learners’ L2 output. The goal of these strategies of L2 teaching is to provide comprehensibility and cognitive stimulation during the L2 acquisition process, induce wide-spread neural activity, and facilitate long-term retention. All of these strategies are exemplified by, and operationalised in, the Teacher Input Observation Scheme (TIOS, Kersten, Bruhn, Ponto, Böhnke, & Greve, 2018), which provides a systematic basis for empirical L2 classroom observation, teacher training and teachers’ self-evaluation. The article closes with empirical and practical examples of the effects of L2 instructional strategies in pre-school and primary school.