The question of race among Puerto Ricans in the United States in the 20th century is explored in this paper. The multiracial character of Puerto Ricans is examined by reviewing Puerto Rico's migration history. Eighteen major works written between 1917 and 1971 on Puerto Ricans are reviewed to discern common racial themes. The methodology of the major works reviewed is analyzed and seven themes found in the literature are discussed. There are: (1) the question of whether Puerto Ricans are a race or not; (2) the continuum of racial types among Puerto Ricans and corresponding names for these types; (3) the generally more "benign" quality of race relations in Puerto Rico; (4) the harsher racial climate in the United States; (5) personal prejudice and the prejudice of no prejudice in Puerto Rico; (6) the theme of "mistaken identity;" and (7) anticipated assimilation paths. These themes reflect the ongoing conflict of two different racial classification systems, that of the United States and that of Puerto Rico. Six endnotes and 35 references are included. (Author/DB)