Vocational teachers continuously tailor their teaching to changes in occupational practice, technologies, and student diversity. Teacher professional development is crucial for dealing with these changes. A longitudinal study was conducted to study the professional development activities of vocational teachers in the Netherlands. It resulted in a typology of formal and informal professional development activities. This typology consolidates preceding typologies, and specifies these for the context of vocational education. During a two-and-a-half year period, 26 experienced teachers detailed their informal and formal professional development activities in learner reports. The 386 activities identified were grouped in six categories of informal professional development activities and in five categories of formal activities. In total, three quarters of the activities could be characterised as informal, embedded in daily practice. Our typology could encourage vocational schools in facilitating professional development more effectively.