Lithium (Li) isotope ratios have been used as a tool in the Earth Sciences since the 1980s, and the number of articles published has risen rapidly in the last 15 or so years. In modern Earth Sciences, lithium isotope ratios are primarily used as a geospeedometer in studies of high-temperature processes, while in Earth surface geochemistry, Li isotope ratios are used as a present and past tracer of chemical weathering processes, the primary method of CO2 drawdown. Many archives of Li isotopes, in particular marine and terrestrial carbonates, or soil exchangeable fractions, have very low Li concentrations (< 1 ng/g), meaning that analytical methods must perforce have to deal with small amounts of Li in a significant matrix. Therefore, preparation and analysis requires care. This chapter details the main methods, and also lists some of the potential problems and pitfalls, such as matrix, column yield, mass-flow controller instability, background correction, tuning, etc. The column purification and multi-collector plasma analysis methods detailed here can reproduce Li isotope ratios (δ7Li) to an external precision of ~± 0.3–0.4‰ (2sd), which is sufficient to reliably reproduce even quite small perturbations and signals.