The environmental impacts of meat-based pet food (e.g., land and water use, fossil fuel consumption, greenhouse gas production, pesticide and fertilizer use, and impacts on biodiversity loss), are globally significant. Given increasing pet ownership globally, ‘food’ animal use for pet food is rising. However, alternative pet foods based on novel protein sources, such as plants and seaweed, insects, yeast, fungi and laboratory grown meat, are rapidly developing. Vegan pet foods are most developed. These use plant, mineral and synthetic sources to supply necessary nutrients. In 2020 I surveyed 4,060 dog or cat guardians to investigate determinants of pet food purchasing decisions, as well as health, behavioural and other outcomes using different diets. I also surveyed 29 pet food manufacturers to determine whether nutritional soundness and quality control of plant-based pet foods differed from meat-based diets. Results from these and other studies indicate that the healthiest and least hazardous pet foods are nutritionally sound vegan diets. Detailed analysis of feeding behaviour indicates dogs and cats generally find such diets as palatable as conventional diets. And manufacturers of plant-based pet foods appear to adhere to quality control standards at least as good as those used in the creation of conventional diets. The environmental and animal welfare benefits of plant-based and alternative diets are profound. These factors are driving a rapid expansion of this sector.