Software development differs between startups and established companies primarily in their development processes, culture, and resources. Startups often emphasize agility and rapid prototyping, focusing on minimum viable products (MVPs) to validate ideas quickly. In contrast, established companies generally have more structured processes and may prioritize stability and compliance. Startups tend to have limited budgets and a dynamic environment, while established firms benefit from established markets and resources, allowing for long-term project planning and risk minimization.