This chapter investigates membership of interest organizations through the lens of precarious self-employment. First, we aim to identity different ‘types’ of self-employment based on their degree of precariousness. Based on a Latent Class Analysis we construct a four-category typology of solo self-employment (i.e., secure traditional / precarity-prone traditional / secure professional / precarity-prone professional). Second, we study whether these different types of self-employed workers have diverging expectations of interest organizations, and/or diverging membership patterns. We use insider-outsider theory to formulate hypotheses on whether precarity-prone self-employed relative to more secure self-employed are organized differently – if they are organized at all. The hypotheses are tested using survey data from the Netherlands. We conclude that the most notable group of self-employed are the precarity-prone professionals, who are not only most likely to deviate from traditional patterns of interest representations, but also most willing to join a trade union.