Background: Spasticity is a common symptom of multiple sclerosis (MS), often leading to functional limitations and disability. Objectives: The aim of this study was to develop a conceptual model of spasticity in MS that integrates the experience of persons with MS (pwMS) and clinicians. The model was developed in accordance with Food and Drug Administration guidance on patient-focused drug development. Methods: A draft conceptual model was developed based on a targeted literature review of published articles from 2014 to 2019 and input from three clinical experts recognized as thought leaders in the field of spasticity (MC, FB, EFF). The model was further developed based on one-time interviews with three clinicians experienced in spasticity treatment or research and semi-structured interviews with 20 adults diagnosed with MS for ?12 months who had spasticity for ?6 months. Patient interview data were collected until concept saturation (evidence that no new information is being provided on successive interviews) was achieved. The model was further refined through iterative feedback from the three clinical experts. Results: Of 282 abstracts reviewed, 23 full-text articles were used to develop the draft conceptual model. The interviewed pwMS were on average 47.3 ± 9.6 years of age (median 47.0, range 33.064.0 years), had been diagnosed with MS for an average of 11.6 ± 8.8 years (median 9.9, range 1.336.0 years), and had self-reported spasticity for an average of 12.3 ± 9.5 years (median 10.0, range 0.636.7 years). Key concepts of the integrated spasticity model included objective manifestations; subjective patient experiences; triggers; moderators; physical, functional, emotional, and social impacts; and long-term consequences. Spasms, pain, and stiffness were the descriptors of spasticity most frequently endorsed by both pwMS and the literature. Some pwMS had difficulty distinguishing spasticity from other MS symptoms (e.g., muscle weakness). Some triggers, emotional impacts, quality of life impacts, and long-term consequences of spasticity reported by pwMS were not discussed in the reviewed literature. Conclusions: Spasticity in MS is complex, multidimensional, and heterogeneous. Clinicians and pwMS may use different descriptors. The integrated conceptual model developed in this study, which includes the perspectives of both pwMS and clinicians, may enhance future research and management of spasticity in pwMS.