Parts of speech in Modern Hebrew are analyzed in relation to three categories: Open Class items (Nouns, Verbs, Adjectives), Closed Class paradigmatically organized grammatical items (e.g., Pronouns, Case-Markers, Conjunctions), and Intermediate elements lying between the two (e.g., Prepositions, Adverbs, Floating Operators). The chapter considers what is meant by "a word" in Hebrew, taking into account the contrast between older and more current items as well as between conventional dictionaries and the mental lexicon, and the critical role of morphology in the Hebrew lexicon. The verb lexicon is characterized by types of consonantal roots (full versus defective) and the binyan conjugation patterns or prosodic templates. Nouns and adjectives are described as morphologically less restricted than verbs, including loan words that are partially integrated into the Hebrew phonological system, generally not constructed by the nominal morphological patterns (miškalim 'weights'). So-called "function words", traditionally grouped together under the label particles and analyzed here as members of either closed or intermediate classes of items, are also typically morphologically non-derived. The chapter concludes by summarizing current trends in lexical innovation in relation to productivity in the MH lexicon.