Background and aim: Children's vegetable intake is far below that recommended. Despite increased awareness of the importance of vegetable consumption for health, it remains challenging to improve children's vegetable intake. Since food preferences are central to food intake, it is important to understand how they are shaped and which factors play a role in this. So far, research on the formation of vegetable preferences has focused mainly on infants and school age children but is not elaborately investigated in toddlers/pre-schoolers. Therefore the aim of this thesis was to investigate the underlying mechanisms and modifying factors that play a role in developing 2-5-year-old children's acceptance of vegetables. Effects of different learning mechanisms, strategies, and modifying factors were explored by diverse studies, including four intervention studies in ecological settings (day-care centres and at home). In another study, we compared 10 intervention studies across Europe. Methods: We conducted a series of day-care and in-home interventions. Healthy toddlers and pre-school children participated in the studies. Vegetable liking was measured by relative preference, and consumption was measured by (ad libitum) intake. First, we studied the underlying mechanisms - flavour-nutrient learning, flavour-flavour learning, and repeated exposure - involved in the development toddlers' food preferences in the short and long term. Novel products like green vegetable soups and vegetable crisps were used as test products, using within-subject designs. The soups differed in energy density to test flavour-nutrient learning (n=28), and the crisps were offered with different dips to test flavour-flavour learning (n=39). Next, we investigated the efficacy of other strategies like taste modification (n=103) and choice-offering (n=70) on 2-5-year-old children's vegetable liking and intake, using between-subjects designs. Children consumed different vegetable products at home at dinnertime and therefore we used more familiar vegetables as test products. Finally, we combined the results of 10 intervention studies across Europe to explore the influence of individual child characteristics such as breastfeeding history and breastfeeding duration, age, gender, and food neophobia on 2-6-year-old children's (n=750) actual vegetable intake. Results: We found a clear and persistent effect of repeatedly offering novel and/or disliked vegetables on 2-5-year-old children's intake. Results for preferences were inconsistent across the studies. We found no strong evidence that strategies such as flavour-flavour learning, flavour-nutrient learning, diluting/hiding a vegetable were more effective in changing vegetable preference than repeated exposure alone. We observed a small positive effect of choice-offering; this strategy could possibly be effective in somewhat older children who already like vegetables, to increase their consumption volume. Factors like breastfeeding duration, vegetable liking, and food neophobia were important for children's vegetable intake. Children who were more reluctant to try novel food had lower vegetable intake and were not responsive to strategies like repeated exposure, blending, mixing, or hiding vegetables. Longer breastfeeding duration was positively associated with a higher vegetable intake by 2-6-year-old children across three European countries. Gender and age had no influence. Conclusions: This thesis demonstrates that repeatedly offering a novel or disliked vegetable in a trusted positive environment is highly effective in promoting toddlers' and pre-school children's vegetable intake. Repeated exposure seems to be the way to teach young children to accept novel or disliked foods. Other strategies such as flavouring, adding energy, or taste modification may be helpful in promoting young children's willingness to try and taste vegetables. Additional strategies such as choice-offering are needed to promote intake of already liked/familiar vegetables when children get older. Individual differences in child characteristics such as food neophobia, breastfeeding duration, and age play a role in shaping food preferences and therefore should get more attention in strategies to promote children's vegetable acceptance.