The first part of this thesis explores and describes the approach to classification of adjectives in Croatian language textbooks for primary and secondary schools. A comparative method provides information on the division of adjectives to classes within the meaning of the textbooks. Interpretation of the adjectives in the elementary and high school textbooks leads to spotting inconsistencies within these books. It was noted that textbooks do not divide adjectives within the meaning equaly. Most primary school textbooks divide adjectives to descriptive and possessive (sometimes building, but rarely), while high school textbooks divide adjectives to descriptive and demonstrative. Also, in a number of textbooks, examples of adjectives do not correspond to the division. The second part of the thesis consists of the analysis of the problems within the morphological and syntactic point of view. It analyzes the classification and declension of adjectives in the context of morphology and determination category within the syntax. This underscores the uneven and wrong division of adjectives to classes, and incorrect connection of definiteness with declension. It is proposed to accept the division of adjectives within the meaning to descriptive and demonstrative. It underlines the importance of defining the category of definiteness in the context of syntax and semantics. It is proposed to separate the adjective declensions of the category of definiteness, because declension is a morphological category. The thesis also proposes the division of the adjective declensions to the adjective-noun and adjective-pronoun.