This article presents a categorization of the phenomena and representations used to introduce negative numbers in mathematics books published in Spain during the 18th and 19th centuries. Through a content analysis of fourteen texts which were selected for the study, we distinguished four phenomena typologies: physical, accounting, temporal and mathematical. Four types of representations are also identified: verbal, numeric, graphic and algebraic. These results reflect the same level of understanding and treatment of negative numbers in Spain as is found in other European countries during this time period. (Contains 3 figures.)