SNOMED International: The Systematized Nomenclature of Medicine 
A dynamic, sustainable, scientifically validated terminology developed by College of American Pathologists (CAP) to enable the sharing of health care knowledge across clinical specialties and sites of care. Includes news, events, services, programs, related sites, training, careers and details of user groups.
http://www.snomed.org/Unified Medical Language System (UMLS)
Metathesaurus and semantic network with lexical applications that can be used to overcome problems caused by differences in terminology and scattering of related information across databases. Includes FAQs, documentation, papers, license agreements, knowledge source server, bibliography and details of applications. (Custodians are the National Library of Medicine)
http://www.nlm.nih.gov/research/umls/
Logical Observation Identifiers Names and Codes (LOINC)
Dataset of universal identifiers for laboratory and other clinical observations to facilitate exchange and storage of clinical results or vital signs for patient care and research. Includes downloads, news, meetings, background, articles, e-mail list and submissions. Links to its custodians the Regenstrief Institute.
http://loinc.org/
National Centre for Classification in Health
Australian centre of excellence in health classification theory and an expert centre in clinical coding systems. (Home of ICD10-AM).
http://www2.fhs.usyd.edu.au/ncch/
Classifications and Terminologies Working Group (CTWG)
Committee of the Australian National Health Information Group (NHIG) with responsibilities for endorsing and monitoring the stability and viability of health classifications and terminologies within Australia. Details of membership, informatics resources, terms of reference, contact information and publications provided.
http://www.aihw.gov.au/committees/ctwg/
OpenGALEN
An open source terminology with tools, expertise and experience in building and delivering a multiaxial medical concept model and terminology.
http://www.opengalen.org/
Medical informatics at Mayo Clinic
Details the LexGrid project, for standardizing the storage and access of medical terminologies. Provides tools, standards and content details.
http://informatics.mayo.edu
