Nickel (Ni) is fundamentally important to the modern world for stainless steel, specialty alloys, electroplating, batteries, and other uses. Global Ni demand is expected to soar as the world transitions to a net-zero greenhouse gas emissions economy based on electric vehicles and energy storage batteries linked to renewable energy systems. This means that understanding the current Ni sector, especially known Ni resources, reserves, and mining (i.e., current and likely future sources of this metal), is crucial to enabling this energy transition, including the likely environmental, social, and governmental challenges that may prevent the development or may hinder the continuation of future and current Ni mining operations. This paper achieves this by presenting a comprehensive global assessment of reported Ni deposits and projects for the year 2018. All of these are classified by mineral deposit type to understand the relative importance of the different mineral systems that are mined for Ni and allocate each site a primary and secondary mineral deposit type. We also compare our results for 2018 with the results of a previous study focused on 2011 data to understand how deposits and projects have evolved over time and coincident with production. The majority of Ni has been and will continue to be sourced from laterites and magmatic sulfide systems; other deposits have produced only minor amounts of Ni. Our database indicates that globally some 627 Ni deposits remain with in-ground resources and/or reserves, including 148 and 86 laterite, 248 and 93 magmatic sulfide, 33 and 14 hydrothermal, and three and two tailings Ni-containing code-and noncode-compliant resources, respectively. Projects with reserve estimates include 38 laterite reserves, 70 magmatic sulfide, and three hydrothermal Ni-containing reserves. These data yield 350.2 million metric tonnes (Mt) of contained Ni in resources distributed as 190.2, 124.1, and 35.4 Mt Ni in laterite, magmatic sulfide, and hydrothermal resources, respectively. Reserves contain 47.12 Mt of Ni split into 25.97, 20.14, and 1.01 Mt Ni in laterite, magmatic sulfide, and hydrothermal reserves, respectively. Comparison of these data to 2011 data indicates that sulfide deposits are effectively keeping pace with depletion by mining, whereas laterite resources are lower than in 2011, perhaps reflecting the fact that the latter can be more comprehensively assessed during the early stage of laterite resource and reserve estimation. This suggests that although current resources are sufficient to enable current production to be sustained, the expected increase in demand for Ni may act to constrain supply. This may also be exacerbated by the increasing environmental, social, and governmental challenges facing the minerals industry globally, with a number of projects that have faced delays or problems associated with these challenges also outlined in this study. Our study also highlights the variable level of sustainability reporting undertaken by different companies involved in Ni mining and exploration. One potential approach to more effective environmental and social engagement would be improvements in this area, allowing more transparent engagement with social and environmental stakeholders. Overall, known Ni resources and reserves are sufficient to continue current levels of production for several decades to come (assuming all of this material can be mined); however, the Ni mining sector faces a number of challenges that may change this, including increased demand from electric vehicles and batteries and potential supply restrictions relating to increased environmental, social, and governmental challenges to the mining industry globally.