The grammar of the Hittite language has a highly conservative verbal system and rich nominal declension. The language is attested in cuneiform, and is the earliest attested Indo-European language.

Hittite distinguishes between two genders, common (animate) and neuter (inanimate). The distinction between genders is fairly rudimentary since it is made only in the nominative and accusative case, and the same noun is sometimes attested in both genders. It is still debated whether or not this reflects a prehistoric merger of inherited PIE masculine and feminine into a single common/animate gender or an archaic system in which there was already a common gender. Nouns referred to living beings (humans, animals and Gods) are usually found in the common/animate gender, but some inanimate objects actually have the common/animate gender. For instance, nouns in a-stem and t-stem are common/animate and, given how productive was the formation of words in the a-stem and t-stem, many words in Hittite indicating inanimate objects are actually in the common/animate gender in the nominative and accusative. The other gender, the neuter/inanimate, is referred to objects, including parts of the body, and abstract concepts or collective nouns, e.g. "family, assembly, troops, humanity". Some common examples of neuter declension are the u-stem nouns and the nouns formed by the suffixes -ātar, -eššar and the suffix for collective nouns -a(i)-. Words derived by common/animate gender roots through neuter suffixes are neuter.

The only reference to a female gender, which however does not erase the two-gender system "common-neuter gender", is the infix -(š)šara-, used to indicate female gender for humans and deities.

The nominal system consists of the following 9 cases: nominative, vocative, accusative, genitive, dative-locative, ablative, ergative, allative, and instrumental.

Hittite declension system also distinguishes between two numbers (singular and plural) and shows indirect traces of a dual number; due to syncretism, the ending of ablative and instrumental in the plural coincide.

Hittite language is based on split ergativity: when a common/animate noun is the subject of a transitive verb, e.g., "The child eats the apple", the subject is marked by the nominative case. By contrast, when a neuter noun is the subject of a transitive verb, e.g., "The spear kills the soldier", the subject of the sentence is marked by the ergative case; hence, only neuter nouns show the ergative case in their declension, which means that common/animate nouns show 8 cases, while neuter nouns show 9 cases. Inflected adjectives always have the ergative case in their declension, but this case is used only when an adjective is referred to a neuter noun in the ergative case, i.e., followed by a transitive verb; consequently, adjectival declension shows 9 cases. Personal pronouns as the subject are always in the nominative case; the subject of an intransitive verb always take the nominative ending as well.

The basic scheme of suffixation is given in the table below, which is valid for almost all nouns and adjectives. The sample word shown is antuḫšaš, "man", a-stem noun (common/animate gender, thus a name without the ergative case). The letter "š" is always pronounced as /s/, while "z" is always pronounced /ts/ and derives from an ancient */ti/ or */tj/. For instance, in mi-verb declension, the 3rd person singular ending in the present tense -zi according to Hoffner and Melchert comes from an earlier *-ti.

Given that the nominal root ends with the thematic vowel -a and some suffixes starts in a vowel, the final -a in the root is elided (e.g., attaš, "father" > dat-loc. atti, not *attai). Only in some rare instances that represent an innovation, a dat-loc. in -ai is found; some of these instances are foreign words and foreign names.