The adsorption of Li and Cs on CdTe(100) single crystals was investigated using different surface sensitive electron spectroscopies. Low-energy electron diffraction shows a number of surface reconstructions of the clean surfaces, influenced by the Cd/Te ratio. Deposition of Li shows a constant sticking probability, while Cs has a variable sticking probability, characteristic of island growth coalescing at a coverage of a monolayer. Li and Cs both form amorphous monoatomic layers. Large work-function changes of the CdTe surface as a function of Li and of Cs coverage were found at the initial stages of adsorption, indicating that Cs and Li atoms are to a large extent ionized on the surface (100) plane. The initial dipole moments for Cs and for Li were calculated with the Helmholtz equation ${\mathrm{\ensuremath{\mu}}}_{\mathrm{C}\mathrm{s},\mathrm{\ensuremath{\theta}}\ensuremath{\rightarrow}0}$\ensuremath{\approxeq}26 D and ${\mathrm{\ensuremath{\mu}}}_{\mathrm{L}\mathrm{i},\mathrm{\ensuremath{\theta}}\ensuremath{\rightarrow}0}$\ensuremath{\approxeq}3.2 D and using Topping plots ${\mathrm{\ensuremath{\mu}}}_{0,\mathrm{C}\mathrm{s}}$=127.2 D and ${\mathrm{\ensuremath{\mu}}}_{0,\mathrm{L}\mathrm{i}}$=4.22 D. Adsorption of oxygen on the cesium-covered surface raises the work function by \ensuremath{\Delta}\ensuremath{\varphi}=0.5\ifmmode\pm\else\textpm\fi{}0.05 eV. Reflection-electron energy-loss spectra of the cesiated CdTe(100) surface at ${\mathit{E}}_{\mathit{p}}$=100 eV, recorded at a low temperature (96 K), show a characteristic Cs two-dimensional surface plasmon, \ensuremath{\Elzxh}${\mathrm{\ensuremath{\omega}}}_{\mathit{s}}$ at 2.05 eV, which disappears with rising temperature. During Cs growth a loss is observed at 26.6 eV which is assigned to Cs 5s core-level transitions.