Organo-alkali metal reagents are essential tools in synthetic chemistry. Alkali metal organometallics aggregate in solution and solid-state forming clusters and polymers. The structure of these aggregates and their structure–reactivity relationship have been of great interest for many decades. This Perspective will look at the strategies that have been employed to isolate low aggregates and, in particular, monomeric complexes of the most common alkali metal alkyls (M = Li–Cs, R = methyl, trimethylsilylmethyl, bis/tris(trimethylsilylmethyl), butyls and benzyl) and the relationship between level of aggregation, structure and reactivity.