Crop production by smallholder farmers in Malawi is characterized by cultivation of maize on a large share of the agricultural land with limited nutrient input. There is need for productive farming systems that are better adapted to a changing climate, and that produce more diverse food to achieve both food and nutrition security. The aim of this thesis was to explore options for sustainable intensification and diversification of maize-based farming systems in central Malawi with legumes and sweet potato.Farmers participating in on-farm soybean agronomy trials ranked eight technologies in descending order of preference as 1. Early planting 2. Plant population 3. Variety choice 4. Compost manure 5. Weeding 6. Inoculant 7. Fertilizer and 8. Spraying. A combination of inoculation, inorganic fertilizer (10 N, 8 P, 20 K in kg ha-1), and 6 t ha-1 compost manure increased yields from 0.86 t ha-1 under farmers’ practice to 1.56 t ha-1 and resulted in average profits of 222 USDha-1. Increased plant populations and biocide spraying also increased yields. Low investment costs make inoculants, compost manure and increased plant populations interesting options, unlike inorganic fertiliser. Locally sourced soybean varieties obtained a larger %Ndfa (65%) than the ‘improved’ variety Nasoko (53%). The %Ndfa was positively associated with soil sand content, sowing date, plant population and biomass accumulation. Quantities of N2 fixed differed between regions and years, and was enhanced by applying inoculant and fertiliser together, leading to more biomass accumulation and larger grain yields. Soil available P and exchangeable K contents also increased the total amount of N2 fixed. Average yield in continuous maize was 2.5 t ha-1, while maize after soybean produced 3.5 t ha-1. Fields of soybean and maize that received adequate nutrient inputs and good management to ensure good yields benefitted most in terms of quantities of N2 fixed by the legume and the yield response of the following maize crop. Evaluation of six orange-fleshed sweet potato varieties on 221 farmers’ fields showed large variability across fields. The average attainable fresh root yield ranged from 18 t ha-1 for variety Zondeni to 32 t ha-1 for Mathuthu, against actual yields of 5 to 9 t ha-1. Elevation, planting date, rainfall and crop establishment could explain only 28 percent of the average yield gap. Varieties differed in average yields and taste preferences.Timely planting was crucial to attain good root yields by making better use of the available rainfall. Kaphulira was most affected by weevils and weevil control is required for market-oriented producers. Male host farmers received better viquality cuttings and planted in better soil moisture conditions, resulting in better establishment and vine yields.In multi-location input trials excellent mean trial yields of 5.0 t ha-1 for maize, 3.4 t ha-1 for soybean, 2.5 t ha-1 for groundnuts and 13.2 t ha-1 for sweet potato were achieved.Responses to various combinations of inorganic fertilizer and lime were highly variable, but applications enhanced yields in all crops. Although maize production and investments in maize fertilizer were not as profitable as the other crops, fertilizer application to maize gave the best returns of food per amount of money invested. Investments in fertiliser and lime in soybean was more worthwhile than in groundnut, though the financial benefits were somewhat hidden by high groundnut prices. While there is potential to derive better financial returns from diversification and intensification with legumes and sweet potato, farmers prioritize maize in terms of land area and resource allocation. The participatory research approach demonstrated that there is a wide range of technologies with different levels of human and financial investment costs that smallholder farmers can adopt to enhance yields and profits. There is large variability between farmers in the potential for adoption and the benefits that can be derived from sustainable intensification. Approaches to enhance crop diversification and intensification should address the main constraints of lack of awareness of the benefits of nutrient application to legumes and sweet potato, unstable markets, and access to inputs and credit.