The pursuit of lexicography is divided into two related disciplines:
Practical lexicography is the art or craft of compiling, writing and editing dictionaries.
Theoretical lexicography is the scholarly discipline of analyzing and describing the semantic, syntagmatic and paradigmatic relationships within the lexicon (vocabulary) of a language, developing theories of dictionary components and structures linking the data in dictionaries, the needs for information by users in specific types of situation, and how users may best access the data incorporated in printed and electronic dictionaries. This is sometimes referred to as metalexicography.
A person devoted to lexicography is called a lexicographer.
General lexicography focuses on the design, compilation, use and evaluation of general dictionaries, i.e. dictionaries that provide a description of the language in general use. Such a dictionary is usually called a general dictionary or LGP dictionary. Specialized lexicography focuses on the design, compilation, use and evaluation of specialized dictionaries, i.e. dictionaries that are devoted to a (relatively restricted) set of linguistic and factual elements of one or more specialist subject fields, e.g. legal lexicography. Such a dictionary is usually called a specialized dictionary or LSP dictionary.
There is some disagreement on the definition of lexicology, as distinct from lexicography. Some use "lexicology" as a synonym for theoretical lexicography; others use it to mean a branch of linguistics pertaining to the inventory of words in a particular language.
It is now widely accepted that lexicography is a scholarly discipline in its own right and not a sub-branch of linguistics, as the object of study in lexicography is the dictionary.
Practical lexicographic work involves several activities, and it is important to note that the compilation of really crafted dictionaries require careful consideration of all or some of the following aspects:
Profiling the intended users (i.e. linguistic and non-linguistic competences) and identifying their needs
Defining the communicative and cognitive functions of the dictionary
Selecting and organizing the components of the dictionary
Choosing the appropriate structures for presenting the data in the dictionary (i.e. frame structure, distribution structure, macro-structure, micro-structure and cross-reference structure)
Selecting words and affixes for lemmatization as entries
Selecting collocations, phrases and examples
Choosing lemma forms for each word or part of word to be lemmatized
Defining words
Organizing definitions
Specifying pronunciations of words
Labeling definitions and pronunciations for register and dialect, where appropriate
Selecting equivalents in bi- and polylingual dictionaries
Translating collocations, phrases and examples in bi- and polylingual dictionaries
Theoretical lexicography concerns the same aspects, but lead to the development of principles that can improve the quality of future dictionaries, for instance in terms of access to data and lexicographical information costs.
Recommended reading
Introductory books on lexicography:
Landau, Sidney, Dictionaries: The Art and Craft of Lexicography, 2nd ed., 2001
Bergenholtz, Henning/Tarp, Sven (eds.): Manual of Specialised Lexicography, 1995
Bejoint, Henri, Modern Lexicography: An Introduction, 2000
Hartmann, R. R. K., Teaching and Researching Lexicography, 2001
Hartmann, R. R. K./James, Gregory (comps.): Dictionary of Lexicography, 1998/2001
Nielsen, Sandro: The Bilingual LSP Dictionary, 1994