This document provides an overview of test specifications and the process of writing test items and tasks. It discusses key aspects of developing test specifications, including how specifications are developed through an iterative process of reverse engineering existing tests and identifying archetypical test questions. Specifications evolve over time through critical analysis and discussion. When writing new items and tasks, test developers should use an evidence-centered design approach to ensure items adequately measure the target constructs defined in the specifications. The goal is to design tests where responses provide valid evidence about test takers' abilities as defined by the specifications.