###### Abstract  
A prerequisite for establishing fusion power as one of the sources for low-carbon electricity generation is the demonstration of the capability of future fusion power plants in achieving tritium self-sufficiency and its capability of efficiently producing electricity; both these functions are related to breeding blanket systems, a key component in the transition from ITER to the first generation of nuclear reactors. The future demonstration of fusion power plants should be the first to show the possibility of delivering several hundred megawatts of electrical energy in net and operate in a closed fuel cycle by using a breeding blanket system. With ITER construction moving forward, DEMO projects are transitioning from a preconceptual to conceptual phase, moving towards the beginning of an engineering phase in about ten years. New material developments and novel manufacturing processes have made their way into blanket design, raising the hopes for more cost-effective designs that still benefit from the high cooling capabilities of complex structures. The presence of the test blanket modules (TBMs) program in ITER has also brought about a paradigm change with respect to the way breeding blanket concepts are developed and nuclear licensing, with quality and qualification requirements now being an important part of the process. This topical collection aims to provide an overview of the current status of breeding blanket designs as well as the main related technological aspects. A total of six papers were published in this Special Issue, mainly addressing various aspects of the design studies for the European DEMO Breeding Blanket. In one of the papers, [PERSON] et al. [1] presents the rationale behind the design choices for the Water-Cooled Lithium Lead (WCLL) blanket concept as well as its main characteristics at the end of the pre-conceptual design phase. Using a holistic approach that simultaneously takes into consideration the influence of neutronics, thermal-hydraulics, thermo-mechanics, and magneto-hydro-dynamics, the resulting WCLL layout is compliant with the imposed requirements in terms of integration, tritium self-sufficiency, cooling capabilities, and mechanical stress limits. The paper concludes with a summary of the main achievements reached during the pre-conceptual design phase, and some remaining open issues are presented. While remaining in the area of WCLL design, [PERSON] et al. [2] moves the discussion towards the qualification of novel manufacturing technologies presenting the preliminary design of an experiment dealing with a more general issue of the fusion breeding blanket, namely tritium permeations from the breeding zones into the blanket cooling circuit that also acts as a Primary Heat Transfer System (PHTS) for a DEMO plant. In this paper, the authors introduce the preliminary engineering design of a WCLL Breeding Blanket mock-up to thoroughly investigate the permeation of hydrogen isotopes from the breeder zone into the PHTS water pipes in the presence of a alumina coating acting as an anti-permeation and corrosion barrier. The paper also includes a hydrogen isotope transport analysis of the mock-up, taking in account the planned testing conditions as well as specific elements coming from the mock-up integration in the TRIEX-II experimental facility. [PERSON] et al. [3] provide an interesting overview of recent activities concerning the fabrication processes and their impacts on the properties of the EUROFER97 steel, which has been selected as the DEMO breeding blanket's structural material. The paper discusses various fabrication routes with a focus on their robustness and applicability in normal industrial processes. The most relevant results of the recent studies on heat treatment, fusion welding, machining, and solid-state bounding of EUROFER97 are included in the paper. As part of a new design strategy, [PERSON] et al.