European citizens continue to engage in solidarity activities in support of vulnerable groups within and beyond their own countries. Many of these organised practices of transnational solidarity provide research with important insights into the features and conditions of organisational forms of support. This article makes use of a unique dataset of transnational solidarity organisations in eight European countries during a period of economic recession and immigration crisis, and aims to empirically describe the different forms and types of solidarity prevalent within three different organisational sectors. It strives to identify the organisational features explaining the elective affinities between organisational forms and solidarity approaches. The empirical analysis validates that organisational traits and types matter when favouring vertical and/or horizontal forms of support towards vulnerable groups. Findings corroborate the relevance of professionalisation, aims, and values, in addition to action repertoires to explain organisational profiles and collective approaches to solidarity-based practices.