This webinar provided an introduction to the design of N-of-1 trials, covering the fundamental principles of individualised trial design and their application in healthcare research. Presented by Dr Suzanne McDonald, the session explored the defining features of N-of-1 trials, illustrated key design concepts through practical examples, introduced other single-case experimental designs, and highlighted important methodological developments that have shaped the field over the past decade. This webinar was the first in a two-part series and is complemented by the follow-up webinar on the analysis of N-of-1 trials.