This review discusses the progress in using superconducting circuits based on Josephson junctions to implement atomic physics and quantum optics experiments. These circuits, which exhibit macroscopic quantum coherence, can behave like artificial atoms and have been used to demonstrate various phenomena analogous to those in natural atoms, as well as unique phenomena not occurring in natural atoms. The review highlights the potential of superconducting circuits in achieving ultrastrong coupling between qubits and photons, enabling cavity quantum electrodynamics, and performing frequency conversion and lasing. It also covers techniques for cooling artificial atoms, generating single and multi-photon states, and performing quantum state tomography. The review concludes by discussing future prospects, including testing quantum mechanics on a macroscopic scale and exploring new phenomena such as the dynamical Casimir effect and coherent population transfer.This review discusses the progress in using superconducting circuits based on Josephson junctions to implement atomic physics and quantum optics experiments. These circuits, which exhibit macroscopic quantum coherence, can behave like artificial atoms and have been used to demonstrate various phenomena analogous to those in natural atoms, as well as unique phenomena not occurring in natural atoms. The review highlights the potential of superconducting circuits in achieving ultrastrong coupling between qubits and photons, enabling cavity quantum electrodynamics, and performing frequency conversion and lasing. It also covers techniques for cooling artificial atoms, generating single and multi-photon states, and performing quantum state tomography. The review concludes by discussing future prospects, including testing quantum mechanics on a macroscopic scale and exploring new phenomena such as the dynamical Casimir effect and coherent population transfer.