In this chapter, we address basic issues associated with count data for the simple cases of two-dimensional tables and simple logistic regression. For a more elementary discussion of two-dimensional tables and simple logistic regression including substantial data analysis, see Christensen (Analysis of variance, design, and regression. Chapman and Hall (1996) Chapter 8 or (2015), Chaper 5 and Section 20.1). In fact, we assume that the reader is familiar with such analyses and use the topics in this chapter primarily to introduce key theoretical ideas. Chapter 15 introduces graphical methods (Correspondence Analysis) for representing residuals in two-dimensional tables, but the mathematics required there is substantially more sophisticated than that used here. The graphical methods are most useful for large tables.