ransient absorption spectroscopy is one the most popular methods to study photochemistry and photophysics. This technique allows observation of the dynamics in the electronic excited states after photoexcitation over a wide range of timescales, from the femtosecond to the millisecond timescales. The probed relaxation dynamics involve multiple channels in competition, such as internal conversion, intersystem crossing, fluorescence, energy transfer, electron transfer, proton-coupled electron transfer, and chemical reactions. The aim of this chapter is to provide general background and discuss state-of-the-art experimental techniques for transient absorption measurements. This will be illustrated by recent applications to study photoinduced processes in inorganic systems including molecular and hybrid systems, in particular toward renewable energy applications. Desirable developments, by no means exhaustive, will then be discussed to sustain future research.