The overlap of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) has been well documented in FTD patients with co-morbid motor neuron degeneration and in ALS patients with frontotemporal dysfunction. Up to 15% of FTD patients and 30% of ALS patients experience the overlap syndrome. The syndrome may be difficult to identify since patients often present either to a neuromuscular clinic or a memory disorder’s center, each which may have limited expertise in the other specialty. Survival is greatly impacted for both disorders in the co-morbid condition, making identification of this syndrome critical. The clinical characteristics of the overlap syndrome with new diagnostic criteria will be discussed along with screening strategies, including the UCSF Screening battery and clinical neurophysiology techniques. Treatable mimics of this disorder will also be described and management techniques. Neuroimaging findings will be summarized, which show that the frontotemporal impairment in ALS patients lies on a continuum. Identification of the overlap syndrome also provides a unique opportunity to study very early signs of FTD and conversely, very early signs of ALS, to gain greater insight into both disorders.