In the dynamic landscape of Artificial Intelligence (AI), two notable phenomena are becoming predominant: the exponential growth of large AI model sizes and the explosion of massive amount of data. Meanwhile, scientific research such as quantum computing and protein synthesis increasingly demand higher computing capacities. Neuromorphic computing, inspired by the mechanism and functionality of human brains, uses physical artificial neurons to do computations and is drawing widespread attention. Conventional electronic computing has experienced certain difficulties, particularly concerning the latency, crosstalk, and energy consumption of digital processors. As the Moore's law approaches its terminus, there is a urgent need for alternative computing architectures that can satisfy this growing computing demand and break through the von Neumann model. Recently, the expansion of optoelectronic devices on photonic integration platforms has led to significant growth in photonic computing, where photonic integrated circuits (PICs) have enabled ultrafast artificial neural networks (ANN) with sub‐nanosecond latencies, low heat dissipation, and high parallelism. Such non‐von Neumann photonic computing systems hold the promise to cater to the escalating requirements of AI and scientific computing. In this review, we study recent advancements in integrated photonic neuromorphic systems, and from the perspective of materials and device engineering, we lay out the scientific and technological breakthroughs necessary to advance the state‐of‐the‐art. In particular, we examine various technologies and devices employed in neuromorphic photonic AI accelerators, spanning from traditional optics to PICs. We evaluate the performances of different designs by energy efficiency in operations per joule (OP/J) and compute density in operations per squared millimeter per second (OP/mm2/s). Putting special emphasis on photonic components such as VCSEL lasers, optical interconnects, and frequency microcombs, we highlight the most recent breakthroughs in photonic engineering and materials science used to create advanced neuromorphic computing chips. Lastly, we recognize that existing technologies encounter obstacles in achieving photonic AI accelerators with peta‐level computing speed and energy efficiency, and we also explore potential approaches in new devices, fabrication, materials, and integration to drive innovation. As the current challenges and barriers in cost, scalability, footprint, and computing capacity are resolved one‐by‐one, photonic neuromorphic systems are bound to co‐exist with, if not replace, conventional electronic computers and transform the landscape of AI and scientific computing in the foreseeable future.This article is protected by copyright. All rights reserved