Q:

Dictionary of list of dictionary c#

I want dictionary of list of dictionary like this :
Dictionary <string, List<Dictionary<string,string>> field;

But visual studio send me error :

Error CS0305  Using the generic type 'Dictionary' requires 2

How can solve this error (or a better solution for my problem)?

A:

You are missing a bracket at the end:
Dictionary <string, List<Dictionary<string,string>>> field;

A:

TL;DR: You are missing a > in the end of the decleration, but you should use a better solution
You should try to avoid complex data structures which involve generic types inside other generic types and so on and create you own class instead.
For example:
A Dictionary from the name of a guy to Dictionary of phone companies he is a member of to a phone number he has in each company will look like:
Dictionary<string, Dictionary<string, string>> nameToCompanyToNumber;

And following what's going on is more difficult than creating custom classes which are more readable:
class Person
{
    Dictionary<string, string> companyToNumber;

    public string GetPhone(string company)
    {
        return companyToNumber[company];
    }
}

This will make your code more clear:
List<Person> people;
people.First().GetPhone("AT&T");

Instead of:
nameToCompanyToNumber["SomePerson"]["AT&T"];

Which will require you to try to understand what is going on every time and will make the code harder to maintain, this is what OOP is all about.
As for your compilation error, you are missing a > in the end:
Dictionary<string, List<Dictionary<string,string>>> field;

A:

Dictionaries like this work. Although it seems you are missing a closing > which probably causes your problem.
Thus:
Dictionary <string, List<Dictionary<string,string>> field;

Should be:
Dictionary <string, List<Dictionary<string,string>>> field;

One thing though from experience. If you have such complex data types and it is not something quick and dirty you should reconsider things and think about using a class instead. 
At least later on a class will be way more maintainable and less confusing than such a complex dictionary (not only later on, but also if someone else has to modify your code). 

