Project structure is one of the most important decisions in an ASP.NET Core MVC application. A small application may work with a simple folder layout, but as the project grows, mixing database logic, UI logic and business rules in the same place quickly becomes hard to maintain.

A clean structure usually separates entities, data access, web UI and business logic. Entity classes represent database tables, the DataAccess layer contains DbContext and EF Core configurations, while the Web layer handles controllers, views and view models.

This separation makes the application easier to test, extend and refactor. Controllers should coordinate the request flow rather than contain all business logic. Views should only render data, and database queries should stay outside the UI layer.

Using view models is also a key practice. Instead of sending database entities directly to views, creating specific models for forms, lists and details gives you more control over validation, security and presentation.