Background Efficient, equitable health research depends on understanding why people decide to take part. The aims of this overview were to update the version published in 2020, identifying psychosocial influences on participation and mapping them to recruitment research and psychological theory. Methods Searches were undertaken in February 2024. Qualitative, quantitative, and mixed-methods systematic reviews were identified, without language or date limits. Methodological quality was rated using AMSTAR-2, and low-quality reviews were excluded. Barriers and facilitators were identified inductively and mapped to the Theoretical Domains Framework (TDF) and COM-B model, and to empirical recruitment research. Results The update included 70 reviews, including 44 new reviews, covering a breadth of populations and settings, and drawing on 1940 primary studies (1428 unique). We identified 15 facilitators, most commonly: altruism, potential for personal benefit and trust. Incentives and convenie