Compact steep-spectrum (CSS) and peaked-spectrum (PS) radio sources are compact, powerful radio sources. The multi-frequency observational properties and current theories are reviewed with emphasis on developments since the earlier review of O’Dea (PASP 110:493–532, https://doi.org/10.1086/316162, 1998). There are three main hypotheses for the nature of PS and CSS sources. (1) The PS sources might be very young radio galaxies which will evolve into CSS sources on their way to becoming large radio galaxies. (2) The PS and CSS sources might be compact, because they are confined (and enhanced in radio power) by interaction with dense gas in their environments. (3) Alternately, the PS sources might be transient or intermittent sources. Each of these hypotheses may apply to individual objects. The relative number in each population will have significant implications for the radio galaxy paradigm. Proper motion studies over long time baselines have helped determine hotspot speeds for over three dozen sources and establish that these are young objects. Multi-frequency polarization observations have demonstrated that many CSS/PS sources are embedded in a dense interstellar medium and vigorously interacting with it. The detection of emission line gas aligned with the radio source, and blue-shifted Hi absorption, and [OIII] emission lines indicates that AGN feedback is present in these objects—possibly driven by the radio source. Also, CSS/PS sources with evidence of episodic AGN over a large range of time-scales have been discussed. The review closes with a discussion of open questions and prospects for the future.

紧凑型陡峭频谱 (CSS) 和峰值频谱 (PS) 无线电源是紧凑、强大的无线电源。对多频观测特性和当前理论进行了回顾，重点是自早期 O'Dea 回顾以来的发展（PASP 110:493–532, https://doi.org/10.1086/316162, 1998）。对于 PS 和 CSS 来源的性质，存在三种主要假设。 (1) PS源可能是非常年轻的射电星系，它们将在成为大型射电星系的过程中演变成CSS源。 (2) PS 和 CSS 源可能是紧凑的，因为它们通过与环境中的稠密气体相互作用而受到限制（并增强了无线电功率）。 (3) 或者，PS 源可能是瞬态或间歇性源。这些假设中的每一个都可以应用于单个对象。每个群体中的相对数量将对射电星系范式产生重大影响。对长时间基线的自行研究有助于确定超过三打源的热点速度，并确定这些是年轻物体。多频偏振观测表明，许多 CSS/PS 源嵌入在致密的星际介质中，并与其发生剧烈的相互作用。检测到与无线电源对齐的发射线气体、蓝移的Hi吸收和 [OIII] 发射线表明这些物体中存在 AGN 反馈——可能是由无线电源驱动的。此外，还讨论了在大范围时间尺度上具有偶发性 AGN 证据的 CSS/PS 来源。审查以对悬而未决的问题和未来前景的讨论结束。