The concept of mental retardation has been subject to periodic definitional upheavals, and even today there is no consensus as to its meaning (Krishef, 1983; Robinson & Robinson, 1976). The most popular current definition is that of the American Association on Mental Deficiency (Grossman, 1973). The AAMD definition requires deficits in age-appropriate adaptive behavior and lower-than-average general intellectual functioning for a classification of mentally retarded. In practice, however, below-average performance on psychometric measures of intelligence continues to be the main reason for labeling people mentally retarded (Smith & Followay, 1979). Despite these definitional problems, those concerned with the care and treatment of people classified as mentally retarded have consistently indicated that these individuals experience language and communication problems (Krishef, 1983; Robinson & Robinson, 1976; Webb & Kinde, 1967). This is, perhaps, not surprising given that most of the instruments used to measure adaptive behavior or intelligence require linguistic communication (i.e., the use of language to communicate). It is surprising, however, that so little is known about the nature and extent of retarded people's problems in linguistic communication. It is true that a good deal is known about their acquisition of linguistic competence (i.e., knowledge of phonology, syntax, morphology, and semantics), but little systematic research has been conducted into their linguistic communicative competence (i.e., their ability to use language for communication; Rosenberg, 1982). This chapter examines recent efforts to understand linguistic communication in mentally retarded children and adults.