What is the difference between var and dynamic in C#?

var is used for implicit typing of local variables. The compiler determines the type at compile time.

dynamic is used for working with objects whose type is only known at runtime. Type checking and method calls happen during execution.

Characteristic	var	dynamic
Typing	Static (compile-time)	Dynamic (runtime)
Type check	During compilation	During execution
Performance	High (type is known)	Lower (analysis required at runtime)
Restrictions	Only for local variables	For variables, fields, properties, parameters
Application	Convenience, code reduction	Interaction with COM, DLR, Reflection

Example with var:

// Compiler determines that x is of type int
var x = 10;
// Compilation error, as x is defined as int
// x = "hello";

Example with dynamic:

// Type of y is determined at runtime
dynamic y = 10;
// No compilation error, as the check occurs at runtime
y = "hello";
// Calling a method that may not exist; error may occur at runtime
// y.SomeMethod();