The early work of Gilles Grenier, and Walter McManus, William Gould, and Finis Welch concluded that US immigrants who are proficient in the English language have higher earnings than immigrants who are not. In view of the post-1950 changes in the national origin mix of immigrant flows, it is not surprising that these changes "explain" the decline in relative wages across successive immigrant waves. The chapter explains the skill decline into a portion due to changes in the national origin mix. In 1992, Fernando Ramos analyzes the return migration decisions of Puerto Ricans living in the United States. There has been a resurgence of immigration in the United States and in many other countries. There were historic changes in the US wage structure during the 1980s and these changes did not affect all skill groups equally. Many studies have confirmed that there has been an overall decline in the relative skills of successive immigrant cohorts.