The English language is difficult in several ways, beginning with the sheer number of words, some of which have very specific correct usage. This chapter explains the writing topics that create the most challenges for documentation, reporting, and advocacy. In order to understand proper word use (managing all those thousands of words correctly), it is essential to understand the sentence: its components, its requirements, and its possible structures. Many of the errors that appear in professional writing are due to misunderstandings about sentences. Run-on sentences contain too much information for one complete thought. Contractions are combinations of two words, almost always with an apostrophe, for example, it’s. It is a good idea to avoid them unless your agency requires them in order to keep reports short. Some commonly used abbreviations are acceptable in human service writing.