This article focuses on reaction cells for in situ/operando studies of heterogeneous catalysts by ultraviolet-visible (UV-vis) and vibrational (IR and Raman) spectroscopies and mainly focuses on transmission, internal reflection, diffuse reflectance, and scattering techniques. Its objective is to present a general overview of the most common commercial and homemade reaction cell designs, their main design characteristics, and limitations to serve as a guide for their selection or the design of new in situ/operando cells. It will be shown that there are currently many designs for different specific catalytic applications. However, an ideal reaction cell for a wide range of catalytic in situ and operando reaction conditions does not exist (yet), that is, with low dead volume (i.e., for fast dynamic response to process feed changes, within tens of seconds), high temperatures (> 500 degrees C), high pressures (>30 bar), low cost, enough sample capacity (for operando studies, in the tens of mg), good spectroscopic response, resemblance to laboratory scale reactors, and reactor wall inertness, among others.