Organizations benefit from using a wide range of assessments to create, sustain, and improve their services. The Six Dimensions tool calls for classifying assessments on scales that are described by the following poles: (1) Quantitative and Qualitative; (2) Solicitation/Perception and Observation/Behavior; (3); National/Comparative and Local/Unique; (4) Continuity/Longitude and Discontinuity/Exploration; (5) Inputs/Outputs and Outcomes; and (6) System-Oriented and User-Centric. Essential features and examples are provided for each pole. Assigning these classifications to a portfolio of assessment activities can help an organization make deliberate, informed choices about the portfolio’s future. Six assessment archetypes (Logs, Surveys, Interviews, Benchmarking, Usability Studies, and Multi-Type Studies) present distinct defining characteristics, strengths, and opportunities. Although the presentation reflects the context of a university library’s services, the tool has application to any service environment.