This cumulative doctoral dissertation consists of four independent studies in the field of empirical health economics. The thesis deals with the topic of health, environment, and behavior. The studies are united by the practical value of the presented evidence. It could be used for better political and individual decision-making in real-world settings by those interested in ensuring economic growth and sustainability of social security systems, reducing inequalities, and providing equitable and efficient healthcare and early childcare. To assist with these goals Study 1 (Disease and Fertility: Evidence from the 1918--19 Influenza Pandemic in Sweden) looks at how the 1918-19 influenza pandemic influenced fertility behavior; Study 2 (You Can Win by Losing! Using Self-Betting as a Commitment Device: Evidence from a Weight Loss Program) examines individual weight loss behavior in today's obesogenic environment; Study 3 (Providers, Peers and Patients. How do Physicians' Practice Environments Affect Patient Outcomes?) explores how physicians' environments influence their treatment behavior; and Study 4 (Early Childcare and Children's Non-Cognitive Development: An Interdisciplinary Approach) investigates how a change in social environment for young children due to early childcare policy affects their behavior.