The landscape of production technologies for three-dimensional structures is experiencing a significant transformation, driven by advancements in computer-controlled layer-wise material deposition techniques, commonly known as additive manufacturing (AM) or 3D printing. Among the established AM methods, laser powder bed fusion (PBF-LB) has emerged as one of the most prevalent techniques for fabricating metallic materials. In the PBF-LB process, a high-energy-density laser selectively melts and fuses metallic powder particles, enabling the precise creation of complex geometries. The effectiveness of this manufacturing technique is largely influenced by a variety of process parameters, which collectively define the resulting microstructure and, ultimately, the mechanical properties of the produced components. Recent research efforts have increasingly focused on understanding the dynamic processes that occur during PBF-LB, primarily through post-mortem microstructural characterization and advanced simulation models. Various systems have also been developed to investigate critical aspects of the process, such as phase transformations, defect formation, and laser-material interactions, in real-time utilizing high-speed X-rays. However, high-speed X-ray techniques have limitations in bulk characterization, particularly concerning realistic dimensions of three-dimensional printed parts. This limitation highlights the need for alternative methods, such as neutron-based characterization, which offers deeper penetration into metallic materials and provides valuable insights into their internal structures. To address this gap, this thesis aims to establish a neutron-based characterization methodology, detailing the development of the measuring system employed and exploring its potential capabilities. Additionally, it presents fundamental examples that lay the groundwork for future research in this area. In Chapter 2, a novel method for disentangling signals from Bragg-edge imaging for strain characterization in PBF-LB environments is introduced. This approach enables the separation of transmission spectra between the printed specimen and its surrounding powder, and it is extendable to other neutron imaging techniques. Chapter 3 details the development of a downsized PBF-LB system (n-SLM), specifically designed for in-situ and operando neutron characterization. Case studies on operando strain evolution, defect characterization, and temperature mapping illustrate the potential of the device. Subsequent studies capitalize on the capabilities of the n-SLM and are presented in the subsequent chapters. Chapter 4 focuses on the ferromagnetic phase evolution in multi-material 316L and CuCrZr during manufacturing, where operando polarization contrast imaging reveals the significant impact of thermal history on the formation of the ferromagnetic phase. In Chapter 5, in-situ neutron diffraction is employed to study the microstructure evolution during in-situ laser heat treatment on 316L and Al-added 316L, highlighting the potential for locally controlling microstructures through thermal treatments. Finally, Chapter 6 investigates residual stress and crystallographic texture development in 2205 duplex stainless steel during PBF-LB, utilizing neutron diffraction and Bragg-edge imaging to examine residual stress accumulation, texture variation, and the influence of thermal history on texture.