Demand refers to the mobilizing potential in a society for protest; relating to the interest in a society in what a movement stands for. Is the movement addressing a problem people care for? Is there need for a movement on these issues? What personal grievances politicize and translate into political claims, and how? Usually, people who participate in a movement are only a small proportion of those caring about the issue. This is not necessarily a sign of weakness; for a movement to be viable, a large reservoir of sympathizers is needed to nourish its activists. We focus on the social-psychological core of the demand-side of protest, consisting of grievances, efficacy perceptions, identification, emotions, and social embeddedness. Protesters are aggrieved and openly contest established authorities, attempting to change existing power structures. They form the tip of larger masses who feel that their interests and/or values are violated. Indeed, passivity in the face of imperiled interests or violated values is more often the rule rather than the exception. Interestingly, passivity is mainly explained by the absence of theoretically renowned predictors, rather than theoretical approaches for non-participation. Special attention is devoted to theories on non-participation.