Classical nucleation and crystal growth theories describe how nuclei form, become stable after reaching a critical size and then enlarge through monomer attachment. More than two decades ago, non-classical pathways have been proposed for various types of (bio)molecules and materials, which can substantially alter the crystallization kinetics and outcomes. Direct observation of non-classical crystallization of inorganic nanomaterials, including metastable structure-mediated and particle attachment-based pathways that usually occur on the nanoscale, was enabled by in situ liquid-phase electron microscopy. However, it was not until recently that the crystallization dynamics of beam-sensitive soft materials were directly imaged with sufficient spatial resolution, and a level of microstructural understanding of defects and interfaces emerged. This article provides a high-level review of the non-classical crystallization pathways discovered in soft and organic materials and a forward-looking guide for future research. We first analyse how the characteristics of soft materials affect their crystallization pathways and kinetics. We then identify technical approaches to studying the crystallization trajectories of soft materials and discuss strategies to properly select and apply them to different systems. Breakthroughs made in understanding the crystallization of small organic molecules, (bio)macromolecules, colloids and reticular framework materials are examined. Finally, we provide an outlook on the challenges in elucidating soft material crystallization pathways and the opportunities for assisting the design and synthesis of new materials and structures.

经典成核和晶体生长理论描述了核如何形成，达到临界尺寸后变得稳定，然后通过单体附着而扩大。二十多年前，人们已经针对各种类型的（生物）分子和材料提出了非经典途径，这些途径可以极大地改变结晶动力学和结果。原位液相电子显微镜可以直接观察无机纳米材料的非经典结晶，包括通常发生在纳米尺度上的亚稳态结构介导和基于颗粒附着的途径。然而，直到最近，光束敏感软材料的结晶动力学才以足够的空间分辨率直接成像，并且出现了对缺陷和界面的微观结构的理解。本文对软材料和有机材料中发现的非经典结晶途径进行了高水平的回顾，并为未来的研究提供了前瞻性的指导。我们首先分析软材料的特性如何影响其结晶途径和动力学。然后，我们确定研究软材料结晶轨迹的技术方法，并讨论正确选择并将其应用于不同系统的策略。研究了有机小分子、（生物）大分子、胶体和网状框架材料的结晶方面取得的突破。最后，我们对阐明软材料结晶途径的挑战以及协助新材料和结构的设计和合成的机会进行了展望。