This document provides indepth study and support of the "Canadian Language Benchmarks 2000" (CLB 2000). In order to make the CLB 2000 usable, the competencies and standards were considerably compressed and simplified, and much of the indepth discussion of language ability or proficiency was omitted, at publication. This document includes: (1) "Theoretical Bases of the CLB 2000: Definitions and Models" (communicative proficiency, contents of each component of communicative proficiency, and selection of CLB competencies and structure of a benchmark); (2) "Philosophical Bases of the CLB 2000: Views, Principles, Theory, and Research" (language and language use; adult second language learning; the role of grammar, pronunciation, and fluency in defining a benchmark; the relationship between language development and the progression of the benchmarks; and the CLB as a framework for developing curricula and assessment tools); and (3) "The CLB Rating Scales: Principles of Assessment and Evaluation in the CLB" (evaluating speaking and writing performance, evaluating listening and reading performance, and an example using the CLB scales to score a writing task). A glossary of terms is included. Three appendixes contain overview of speaking, listening, reading, and writing benchmarks. (Adjunct ERIC Clearinghouse for ESL Literacy Education) (Contains 171 references.) (SM)