Technical books of each subject area denote the level of maturity and knowledge demand in that area. According to the Google Books database, about 208 Unified Modeling Language (UML) books have been published from its inception in 1997 until 2009. While various book reviews are frequently published in various sources (e.g., IEEE Software Bookshelf), there are no studies to classify UML books into meaningful categories. Such a classification can help researchers in the area to identify trends and also reveal the level of activity in each sub-area of UML. The statistical survey reported in this article intends to be a first step in classification and trend analysis of the UML books published from 1997 to 2009. The study also sheds light on the quantity of books published in different focus areas (e.g., UML's core concepts, patterns, tool support, Object Constraint Language and Model-Driven Architecture) and also on different application domains (e.g., database modeling, web applications, and real-time systems). The trends of book publications in each sub-area of UML are also used to track the level of maturity, to identify possible Hype cycles and also to measure knowledge demand in each area.