The term regression modeling is used loosely here to denote a situation where a disease outcome variable is geo-referenced and is to be related to predictors and/or covariates. These predictors can be observed at different levels of spatial aggregation and can be spatially-referenced or not. Ecological analysis is special case of regression modeling where a relation is estimated at an aggregation level and inference is to be made at a lower aggregation level. In what follows, I do not discuss misaligned (MIDP) or modifiable areal unit problems (MAUP) directly as these are discussed in Chapter 9.