This review article will discuss the application of intrathecal baclofen (ITB) therapy in the upper motor neuron syndrome (UMNS). While the UMNS consists of a variety of signs and symptoms, spasticity appears to be the most widely discussed in research and clinical practice. Thus, while a variety of motor disorders result from spasticity and the other components of the UMNS, such as dystonia, rigidity, and co-contraction of agonists and antagonists, we will refer to spasticity as the representative pathology of the UMNS. The term spasticity will be used in this discussion as if it were synonymous to the UMNS, because it is the term used in most published research and papers. This does not necessarily mean that the other features of the UMNS are less important. Publications in the use of ITB in the pediatric population, especially cerebral palsy, abound, but this paper will focus on UMNS in adults. In addition to reviewing the process of ITB management, from patient selection to rehabilitation, topics of practical interest to clinicians will be discussed.