Gig workers commonly face challenges that differ in nature or intensity from those experienced by traditional organizational workers. To better understand and support gig workers, we sought to develop a measure that reliably and validly assesses these challenges. We first define gig work and specify its core characteristics. We then provide an integrated conceptual framework for a measure of six challenges commonly faced by gig workers—viability, organizational, identity, relational, emotional, and career-path uncertainty. We then present five studies: item generation in Study 1; item reduction, exploratory assessment of the factor structure of these items, and initial tests of convergent validity in Study 2; and in the remaining three studies, we draw from different gig worker populations to accumulate evidence for the convergent, discriminant, and criterion validity of our Gig Work Challenges Inventory (GWCI), and present initial tests of the universality of the gig challenges inventory across a range of socio-demographic, job type, and regional factors. Our findings establish the reliability and validity of a GWCI that can aid researchers seeking to better understand the types and impact of stressors gig workers face, which in turn can help to inform theory, practice, and public policy.