In this article, I analyze recent intellectual debates on the Puerto Rican nation and its persistent colonial relation with the United States. First, I trace the development of a nationalist discourse on the Island, primarily among intellectuals, writers, and artists during the 20th century. I identify several problems with this discourse, especially the exclusion of ethnic and racial others from its definition of the nation. Then I argue that any serious reconceptualization of Puerto Rican identity must include the diaspora in the United States. I focus on the increasingly bilateral flow of people between the Island and the U.S. mainland - what has come to be known as circular, commuter, or revolving door migration. The Spanish folk term for this back-and-forth movement is extremely suggestive: el vaivén (literally meaning fluctuation). La nación en vaivén, the nation on the move, might serve as an apt metaphor for the fluid and hybrid identities of Puerto Ricans on both sides of the Atlantic. My thesis is that massive migration - both to and from the Island - has undermined conventional definitions of the nation based exclusively on territorial, linguistic, or juridical criteria. [cultural identity, diaspora, nationalism, transnationalism, circular migration, Puerto Ricans].