This study analyzes the variables associated with followers' reactions to the Instagram posts of nonprofit organizations (NPOs). We analyzed all the 980 posts published by 58 Spanish nongovernmental development organizations on their Instagram feeds for 5 weeks. The results show that follower engagement, in terms of likes and comments, is associated with organizational characteristics of the NPOs (government grants, internationalization, religiosity), their use of social media (experience on other social media platforms, Instagram activity), and the content of the posts (engagement hierarchy classification, visual content, originality of content, use of interactive tools). For NPOs, these results indicate the importance of being aware of their own characteristics and the need to promote other aspects that they can control (the use of social media and the content they incorporate in their posts) to achieve greater levels of engagement.