In this dissertation, drawing from the Black politics and social movement literature, I develop a theory of “Alienated Activist” movements. In Chapter 1, I argue that the nationalization of Black politics, the constraints of Barack Obama’s presidency, and the quotidian nature of Black death opened a political opportunity for a new mass movement to occur. I claim that Black Lives Matter (BLM) represents a departure from Black “politics-as-usual,” and with other contemporary mass movements, including Occupy Wall Street and the Arab Spring, can be understood as a new social movement type, Alienated Activism. Chapter 2 explains the theory of Alienated Activist movements, which occurred in response to crises in neoliberalism and legitimation in the early 2010s. In three following chapters, I unpack the mechanisms of Alienated Activism, namely, identity, mobilization, and transformation, with a particular focus on BLM. In Chapter 3, “Mobilizing Identity: Assessing Public Support for Black Lives Matter,” I consider how identity influences support or opposition for BLM. Taking an aggregate view, I use national survey data from the American National Election Study and the GenForward Survey of Millennials. I find that movement adherence is consistently determined by politicized identities, especially gender and race. I also find that opposition is motivated by attitudes towards Black Americans—in my models racial resentment. Furthermore, the feeling that police mistreat Black Americans produces support for the movement. This demonstrates that Black Lives Matter elicits a host of feelings amongst Americans; specifically, that movement adherents across racial groups and generations are motivated by identity, racial attitudes, as well as feelings about racial discrimination in policing. In Chapter 4, “Alienated Activism: Activation, Education, and Mobilization,” through 35 interviews with radical, progressive, and racial justice activists in Chicago, I zero in on the local and further theorize the micro- level processes of Alienated Activism. I describe both activists’ orientation towards the state and their forms of political participation. I argue that alienated activists are oriented by 1) their positions of marginality, 2) disillusionment with institutions and political conditions, and 3) via political solidarity. Rather than disengage from politics, however, they pursue political activities rooted in a desire to build collective power in their communities. Through their alienation from the state and via processes of political education, activists participate in 1) relational political activities (such as political organizing), 2) building efficacy in collective movement space, and 3) developing transformative political alternatives. In this chapter, I especially focus on racial justice and Movement for Black Lives activists in Chicago. In Chapter 5 “Framing Police Violence,” I consider how progressives across the United States evaluate various frames and solutions for police violence, testing whether transformative language from recent BLM uprisings has gained support among likely adherents. I consider the discursive transition from reformist to abolitionist language after the uprisings for George Floyd in 2020, comparing progressive support for police reform and police abolition. Police reform is broadly supported across respondents, with very little variation in approval of a “reformist” petition. As for police abolition, I find that younger respondents and those who say they attended a BLM protest after the death of George Floyd in 2020 are more likely to add their name to an abolitionist petition than respondents who are older or those who did not attend a BLM protest. This suggests the BLM movement has made some important progress in advancing its transformative abolitionist frame. This dissertation contributes to both the Black politics and social movements literature, locating the Black Lives Matter movement as an important development in Black politics and advancing a new social movement paradigm, Alienated Activism.