His most notable contribution to translation theory is Dynamic Equivalence, also known as Functional Equivalence. For more information, see "Dynamic and formal equivalence." Nida also developed the componential analysis technique, which split words into their components to help determine equivalence in translation (e.g. "bachelor" = male + unmarried). This is, perhaps, not the best example of the technique, though it is the most well-known.
Nida's dynamic-equivalence theory is often held in opposition to the views of philologists who maintain that an understanding of the source text (ST) can be achieved by assessing the inter-animation of words on the page, and that meaning is self-contained within the text (i.e. much more focused on achieving semantic equivalence).