Amyotrophic lateral sclerosis (ALS) is a devastating incurable neurodegenerative disease that targets motor neurons, manifesting as a linear decline in muscular function and leading to death within 2 - 5 years of diagnosis. The vast majority of ALS cases are sporadic, the aetiopathology of which is incompletely understood. Recent data have implicated the microenvironment of the motor neuron as a primary target of the pathophysiology. Any experimental therapeutic approach to ALS is very difficult because of some peculiarities of the disease, such as the unknown origin, the spatial diffusion of motor neuron loss and the paucity of animal models. Despite such daunting challenges, in experimental models a number of potential benefits of stem cells in ALS therapy have been demonstrated: by providing non-compromised supporting cells such as astrocytes, microglia or growth factor-excreting cells, onset can be delayed and survival increased. Moreover, in animal models of acute or chronic motor neuron injury, neural stem cells implanted into the spinal cord have been shown to differentiate into motor neurons, with some evidence of axonal sprouting and formation of nerumuscular junctions with host muscle. Here we summarise and discuss current preclinical and clinical evidence regarding stem cells application in ALS, particularly focusing on methodological issues.