This article is dedicated to the description of the morphological features of the Romanian language of the 16th-17th centuries, using the manuscript Codex Neagoeanus as an example. The subject of the research is a comprehensive morphological analysis of the manuscript monument "Codex Neagoeanus" (ms. rom. 3821, Romanian Academy Library), dated to the beginning of the 17th century. This codex represents a characteristic collection of religious and folk texts (cărți populare) typical for Romanian culture of the 16th-17th centuries, including translations of a popular romance, a didactic treatise, a brief nomocanon, and works of astrological literature. The study focuses on a systematic description and classification of archaic and variable morphological features of the Romanian language recorded in the texts of the codex. Special attention is given to those features that demonstrate the transitional nature of the language of this era, which is at the intersection of the old Latin tradition and the active influence of Slavic languages, as well as the process of establishing future literary norms. The analysis is conducted using material from all significant parts of speech: nouns, adjectives, verbs, pronouns, and adverbs. The main research method is a comprehensive morphological analysis aimed at identifying and classifying characteristic archaic and innovative elements in the morphological system of the writing monument. Paleographic analysis methods are also employed. The scientific novelty of the research lies in the first detailed and systematic linguistic analysis of Codex Neagoeanus, which introduces new factual material into scientific circulation. Key conclusions include the following: the morphological system of the codex is characterized by extreme variability and the absence of a stable norm, which is manifested in the coexistence of archaic (ending -u for masculine nouns, obsolete forms of the perfect tense) and innovative (periphrastic conditional) forms. It has been established that phonetic processes (e.g., diphthong contraction ea) directly influenced verb conjugation paradigms. An important conclusion is the demonstration of the deep integral influence of Slavic languages, expressed not only in lexical borrowings but also in the active use of Slavic word formation models (suffixes -enie, -nie, prefix ne-) to create new words based on Latin and Greek roots. Thus, the codex serves as a vivid testimony to the complex and multifaceted state of the Romanian language in the early period.