Generics is a concept introduced in .NET 2.0 and these are 
just like templates in C++. Using generics we can create 
classes,methods,events, delegates which work with any type
(like int,string,myclass etc). In .NET 2.0, 
System.Collections.Generic namesapce was introduced and it 
contains classes/interfaces related to generics. Advantages 
are Performance, Code Reuse, Type Safety.

we can create generic classes (which work with any type)
in .NET 1.1 by using System.Object class. But, it requires 
type casting, boxing and unboxing operations internally. 
these operations are very expensive. so performace of 
application will degrade.

They are tad similar to C++ templates. With .net 1.0, 
creating a flexible class or method that should use classes 
that are known at compile time must be based on the object 
class. With the object class, theres no type safety during 
compile time. casting is necessary. Also, using the object 
class for value types has a performance impact. .Net 2.0 
supports generics, with generics the object class is no 
longer necessary in such scenarios. Generic classes make 
use of generic types that are replaced with specific types 
as needed. This allows for typesafety. The 
system.collections.Generic namespace gives you access to 
generic versions of the stack, dictionary,
sorted dictionary, list and queue classes.
Advantages: Binary code reuse, performance, easy of 
reading, typesafety.