Organolithium complexes, such as the organomagnesium Grignard reagents, are important reactants in organic synthesis. The similarity in structure, bonding, and reactivity of organolithium and -magnesium compounds exemplifies the common chemistry exhibited by representative elements that appear in the same diagonal in the periodic table. Although much debate exists over the degree of covalency within lithium–carbon bonding interactions—the presence of some covalent characters in Li–C bonds of alkyllithium compounds is widely accepted. The bonding interactions within organoalkali metal complexes of the heavier alkali metals are generally considered to be strongly electrostatic or ionic in nature. This is supported by a large collection of evidence, consisting primarily of solution NMR data, single-crystal X-ray analyses, and gas-phase computational studies. Many of the organolithium compounds are soluble in hydrocarbons, but organometallic compounds of the heavier Group 1 metals generally require more polar media to dissolve. In general, the reactivity of the alkali metals and the reactivity of the organometallic compounds of these metals increase as the group descends. Although organoalkali metal compounds are similar to Grignard reagents, they are more reactive and are both air- and moisture-sensitive and sometimes pyrophoric. In addition, organoalkali metal compounds will react as Brønsted bases with protic reagents. Specific details regarding the synthesis, reactivity, and structures of various types of organoalkali metal compounds are discussed.