The past 50 years have witnessed achievement of a set of widely attested empirical findings on major research issues in SLA. They pertain to such matters as cross-linguistic influence; processes and sequences in interlanguage development; age effects; incidental and intentional, learning and implicit and explicit knowledge; the role of the linguistic environment and of the broader social context as sources of positive and negative evidence and of opportunities for input, interaction and output; and effects of individual differences in language aptitudes and other cognitive and affect...