Structs define data and methods, while interfaces provide polymorphism. Probably easiest to understand with an example: package main import "fmt" // Define an interface that both structs will implement type Animal interface { Speak() string Move() string } // Dog struct is a type with one field, but they usually have many fields type Dog struct { Name string } // Speak implementation for Dog, matches same function in the interface func (d Dog) Speak() string { return fmt.Sprintf("%s says: Woof!", d.Name) } // Move implementation for Dog, matches same function in the interface func (d Dog) Move() string { return fmt.Sprintf("%s runs around happily.", d.Name) } // Define a similar struct for Cat. Note that the fields here do not need // to be the same as Dog. An interface knows nothing about these fields. type Cat struct { Name string } func (c Cat) Speak() string { return fmt.Sprintf("%s says: Meow!", c.Name) } func (c Cat) Move() string { return fmt.Sprintf("%s gracefully walks away.", c.Name) } // Function that accepts the interface as an argument, in other words, // any struct that has those Speak and Move methods defined func DescribeAnimal(a Animal) { fmt.Println(a.Speak()) fmt.Println(a.Move()) fmt.Println() } func main() { dog := Dog{Name: "Buddy"} cat := Cat{Name: "Misty"} // Both structs satisfy the Animal interface DescribeAnimal(dog) DescribeAnimal(cat) } Answer from axvallone on reddit.com