Why is Dictionary preferred over Hashtable in C#?

Question

In most programming languages, dictionaries are preferred over hashtables. What are the reasons behind that?

Answer 1

According to what I see by using .NET Reflector:

[Serializable, ComVisible(true)]
public abstract class DictionaryBase : IDictionary, ICollection, IEnumerable
{
    // Fields
    private Hashtable hashtable;

    // Methods
    protected DictionaryBase();
    public void Clear();
.
.
.
}
Take note of these lines
// Fields
private Hashtable hashtable;

So we can be sure that DictionaryBase uses a HashTable internally.