A virtual workshop titled Integrating Systems and Sectors Toward Obesity Solutions, held April 6, 2020 (Part I), and June 30, 2020 (Part II), was convened by the Roundtable on Obesity Solutions, Health and Medicine Division, National Academies of Sciences, Engineering, and Medicine. The workshop introduced the concept of complex systems and the field of systems science, and explored systems science approaches to obesity solutions. Speakers provided an overview of systems science theories, approaches, and applications, highlighting examples from within and outside the obesity field. Presentations and discussions examined complex systems in society that have the potential to shape public health and well-being, and considered opportunities for systems change as they relate to obesity solutions. Specifically, the workshop explored factors that can influence obesity - such as (in)equity, relationships, connections, networks, capacity, power dynamics, social determinants, and political will - and how these factors can impact communications and cross-sector collaboration to address obesity. This publication summarizes the presentations and discussion of the workshop.