This lesson provides a technical introduction to Global Navigation Satellite Systems (GNSS), covering theory, procedures, and accuracy issues. Aimed at bachelor-level educated professionals in a “geospatial science” field, including engineers, surveyors, meteorologists, geographers and GIS professionals, it will also be useful for emergency managers, and technically-inclined members of the general public with appropriate math and/or science background. For those who may currently see GPS/GNSS as a “black box”, this 1.5 hour lesson provides an understanding of the underlying principles and concepts to support correctly interpreting GPS results and obtaining accurate measurements under various circumstances.