General Computer Science	Artificial Intelligence
Computational Linguistics

General Computer Science

Computer Science is the art and/or science of dealing with machines.  It is comprized of everything from the physical construction of computers (though that is usually left to Computer Engineers), to the theory of how these machines work, and under what conditions, and what they can be made to do.  Subdisciplines of Computer Science include Networking, Artificial Intelligence, Machine Learning, Computational Linguistics, and so many more that I could not enumerate them given the entirity of my lifetime.  It must suffice to say that Computer Science is the science of computing machines, and be left at that.

• ACM

The Association for Computing Machinery is THE organization for computer scientists and software engineers to belong to, in fact, in most circles, it is the organization to belong to that defines computer professionals in general.
• IEEE

Even though the Institute for Electrical and Electronics Engineers is not really a computer science organization, they have taken several areas of Computer Science, and so I thought it only fair to mention them here.
 

Artificial Intelligence (AI) is generally, the making of Intelligence by artifice, or skill.  This is not constrained to only be using computers, but as computers seem to be the only machine complex enough to have any hope at all of ever actually allowing this, this is the field that AI falls into.  As a side comment, consider the idea that computers be used to further our study of intelligence itself, or more specifically of Cognition.  This is the rather recent field of Cognitive Science.  Even though the two fields are considered at least partially distinct, they are two different approaches more than anything else.  Cognitive Science is more concerned with using Artificial Intelligence techniques in so far as they assist in understanding the underlying concept that we call Intelligence.  Similarly they use the Psychology and Philosophy sciences to assist in their understanding of the underlying concept of intelligence. This is through Psychology's study of human intelligence and Philosophy's study of the pure form of intelligence (more what they are after).

• AAAI

The American Association for Artificial Intelligence is the organization for Artificial Intelligence professionals to belong to.
• IJCAI

The International Joint Conferences in Artificial Intelligence are a group of artificial intelligence organizations that have come together to share ideas.  AAAI, mentioned above, is one of these organizations.
 

Computational Linguistics (CL) is a subdiscipline of Natural Language Processing (NLP).  NLP is concerned with the processing of natural language (language as we use it naturally) but it is not concerned with the science of linguistics.  It will achieve the task for which it is processing natural language by any and all means necessary.  CL is concerned only with NLP where it specifically implements or improves the field of linguistics.  While the two fields are quite similar in what they do, and therefore intertwined, their approach is different, similar to difference between Artificial Intelligence and Cognitive Science.

• ACL

The Association for Computational Linguistics