ECMA-334 C# Language Specification

8.7.10: Static constructors (informative)

A static constructor is a member that implements the actions required to initialize a class. Static constructors cannot have parameters, they cannot have accessibility modifiers, and they cannot be called explicitly. The static constructor for a class is called automatically.

The example 
using Personnel.Data;  
class Employee  
{  
   private static DataSet ds;  
   static Employee() {  
      ds = new DataSet(...);  
   }  
   public string Name;  
   public decimal Salary;  
   ...  
}
shows an Employee class with a static constructor that initializes a static field.