The quiet Sun is the region of the solar surface outside of sunspots, pores, and plages. In continuum intensity it appears dominated by granular convection. However, in polarized light the quiet Sun exhibits impressive magnetic activity on a broad range of scales, from the 30,000 km of supergranular cells down to the smallest magnetic features of about 100 km resolvable with current instruments. Quiet Sun fields are observed to evolve in a coherent way, interacting with each other as they are advected by the horizontal photospheric flows. They appear and disappear over surprisingly short time scales, bringing large amounts of magnetic flux to the solar surface. For this reason they may be important contributors to the heating of the chromosphere. Peering into such fields is difficult because of the weak signals they produce, which are easily affected, and even completely hidden, by photon noise. Thus, their evolution and nature remain largely unknown. In recent years the situation has improved thanks to the advent of high-resolution, high-sensitivity spectropolarimetric measurements and the application of state-of-the-art Zeeman and Hanle effect diagnostics. Here we review this important aspect of solar magnetism, paying special attention to the techniques used to observe and characterize the fields, their evolution on the solar surface, and their physical properties as revealed by the most recent analyses. We identify the main open questions that need to be addressed in the future and offer some ideas on how to solve them.

安静太阳是太阳表面除黑子、孔隙和斑块之外的区域。在连续强度中，它似乎以粒状对流为主。然而，在偏振光下，安静的太阳在广泛的尺度上表现出令人印象深刻的磁活动，从 30,000 公里的超颗粒细胞到当前仪器可解析的约 100 公里的最小磁特征。人们观察到，安静的太阳场以连贯的方式演化，在水平光球流的平流作用下彼此相互作用。它们的出现和消失的时间尺度非常短，给太阳表面带来了大量的磁通量。因此，它们可能是色球层加热的重要贡献者。观察这些场是很困难的，因为它们产生的信号微弱，很容易受到光子噪声的影响，甚至完全隐藏。因此，它们的进化和性质在很大程度上仍然未知。近年来，由于高分辨率、高灵敏度分光偏振测量的出现以及最先进的塞曼和汉勒效应诊断的应用，情况有所改善。在这里，我们回顾太阳磁性的这一重要方面，特别关注用于观察和表征磁场的技术、它们在太阳表面的演化以及最新分析揭示的它们的物理特性。我们确定了未来需要解决的主要开放问题，并就如何解决这些问题提供了一些想法。