Formal and informal systems of evaluation are commonly used by school divisions and districts to monitor teaching staff, measure teacher quality, inform staffing decisions, and plan professional development opportunities. Criticism from educators and supervisors of traditional and nontraditional evaluation systems has raised questions regarding the effectiveness of teacher evaluation in aiding teachers to improve their practices and achieve higher levels of professional growth. When implemented effectively, both formal and informal systems of evaluation have the capacity to support significant improvements in the quality of teaching and learning, and greater success is possible when the core components and guiding principles that form the foundation of the system are fully understood.