The major routes of nickel exposure that have toxicological relevance to the workplace are inhalation and dermal exposures. Oral exposures can also occur (e.g., hand to mouth contact), but the institution of good industrial hygiene practices (e.g., washing hands before eating) can greatly help to minimize such exposures. Therefore, this chapter mainly focuses on the target systems affected by the former routes (i.e., the respiratory system and the skin). To the extent that other routes (such as oral exposures) may play a role in the overall toxicity of nickel and its compounds, these routes are also briefly mentioned. Focus is on the individual nickel species most relevant to the workplace, namely, metallic nickel and nickel alloys, oxidic, sulfidic and soluble nickel compounds, and nickel carbonyl.