I Took Mo's Claim That Day In San Antonio That There Did Not Exist An Authentic Movement As Something Of A Taunt. Was Mo, A Wickedly Intuitive Thinker, Having A Go With A Sociologist Who Had Come To Interview Him About His Role In The Migrant Rights Movement? Was He Feeding Me The Sour Fruit Of His Failed Struggle For Leadership And Recognition In That Movement? Or Did He Understand Something Important That I Was Missing? This Book Is Largely The Result Of My Trying To Square His Claim With Protests On The Ground That Seemed To Me To Be Countouring A Radical And Dynamic Migrant Rights Movement-actions That Included The Dream 30 Border Crossing I Had Just Witnessed. The Empirical Analysis I Present In The Chapters To Follow Challenges And Confirms Aspects Of Mo's Claim. These Chapters Cover A Decade Of Collective Actions Organized By Undocumented Youth. They Chronicle How A Relatively Small Network Of Activists Almost Single-handedly Radicalized A Social Movement. But To Understand How This Happened, Mo's Claim That There Was No Movement Must Be Taken Seriously. If This 'no-movement' Claim Is Contradicted By The Very Actions Organized By Niya And Emulated By Other Organizations, The Activists Who Pulled Off These Influential Protests Managed To Do So Precisely Because They Believed There Was No Real Movement. Defending The Claim That There Was A Social Movement Turns Out To Be A Slippery Intellectual Task. It Is Not Simply A Matter Of Finding Evidence To Answer An Empirical Question. Sociologists Are Not In Agreement About What Social Movements Are. It Is Not Much Of An Exaggeration To Say That No One Knows What A Movement Is. Many Scholars Have Decided To Simply Jettison The Term, And All The Fuzzy Thinking Associated With It, For Alternatives Like Contentious Politics Or Challengers. We Often See Social Movements Where They Do Not Exist. We Extend The Movement Label To Tidily Gather-up A Wide Range Of Collective Actions And Protests That Appear To Advance A Cause For Or Against Social Change. We Turn Otherwise Unconnected Acts, Carried Out By Varied Organizations And Social Networks, Into A Movement With A Unitary Character. Having Tidied Up The Mess Of Disparate Actions, We Conflate Certain Organizations And Social Networks With This Unified Characterization Of A Movement And Make The Organizations And Networks Stand In For The Movement. We Then, In Turn, Credit This Unitary Character With Collective Actions That This Hypostatized Actor Could Have Ever Pulled Off. Charles Tilly And Alberto Melucci, Two Giants In The Sociology Of Social Movements Who Followed Very Different Empirical And Theoretical Approaches, Both Warned Analysts Against These Errors Of Reification When Trying To Explain Social Movements-- Provided By Publisher.