A word, a part of a word or a chain of words that forms the basic elements of the vocabulary of a language is known as a lexical unit. Generally, lexical units convey a single meaning but they are not limited to single words. Lexis refers to the entire store of lexical units in a language. Complex lexical units can be both, compounds and multi-word expressions that are made up of at least two constituents. Compounds are morphological objects and multi-word expressions that arise from syntactic processes. The exact demarcation between these two varies greatly from language to language. This book includes some of the vital pieces of work being conducted across the world, on various topics related to complex lexical units. It strives to provide a fair idea about this discipline and to help develop a better understanding of the latest advances within this field. This book is a vital tool for all researching and studying this field.