  Axionlike particles (ALPs) are a common prediction of theories beyond the
Standard Model of particle physics that could explain the entirety of the cold
dark matter. These particles could be detected through their mixing with
photons in external electromagnetic fields. Here, we provide a short review
over ALP searches that utilize astrophysical $\gamma$-ray observations. We
summarize current bounds as well as future sensitivities and discuss the
possibility that ALPs alter the $\gamma$-ray opacity of the Universe.
