This study investigates the impacts of access to inventory credit (warrantage), input supply shops, fertilizer micro-dosing demonstrations, and other factors on farmers' use of inorganic and organic fertilizer in Niger, and the impacts on crop yields. We find that access to warrantage and input shops and participation in fertilizer micro-dosing demonstrations have increased use of inorganic fertilizer. Access to off-farm employment and ownership of traction animals also contribute to use of inorganic fertilizer. Use of organic fertilizer is less affected by these factors, but is substantially affected by the household's crop mix, access to the plot, ownership of durable assets, labor and land endowments, and participation in farmers' associations. Land tenure influences both inorganic and organic inputs, with less of both on sharecropped and encroached plots. Inorganic fertilizer has a positive impact on millet yields, with an estimated marginal value-cost ratio greater than 3, indicating significant profitability. Organic fertilizer has a positive impact on millet-cowpea yields. We find little evidence of complementarity between inorganic and organic fertilizer. Since warrantage, input supply shops and fertilizer micro-dosing demonstrations increase use of inorganic fertilizer which in turn increases millet yields, these interventions indirectly increase millet yields, although the impacts are relatively small. These findings support promoting increased input use through promotion of inventory credit, input supply shops and fertilizer micro-dosing demonstrations. Other interventions that could help to boost productivity include promotion of improved access to farm equipment and traction animals and improved access to land under secure tenure.