| Name (English / local (abbreviation)) | Founded | Region served | Notes |
| Association against Quackery / Vereniging tegen de Kwakzalverij (VtdK) | 1881 |  Netherlands | Oldest skeptical organisation.[1] Member of ECSO.[citation needed] |
| Association for Skeptical Enquiry (ASKE) | 1997 |  United Kingdom | Member of ECSO.[2] |
| Australian Skeptics | 1980 |  Australia | |
| Center for Inquiry (CFI) | 1991 |  World | Global umbrella organisation based in Amherst, New York. |
| Committee for the Advancement of Scientific Skepticism (CASS) | 2010 |  Canada | Part of Centre for Inquiry Canada. |
| Committee for Skeptical Inquiry (CSI), formerly Committee for the Scientific Investigation of Claims of the Paranormal (CSICOP) | 1976 |  United States | Part of the Center for Inquiry. |
| Committee Para / Comité Para[3] | 1949 |  Belgium | Member of ECSO.[2] Serves Wallonia and Brussels. |
| Czech Skeptics Club Sisyfos / Český klub skeptiků Sisyfos (Sisyfos) | 1995 |  Czech Republic | Member of ECSO.[2] |
| Dakshina Kannada Rationalist Association / தட்சிண கன்னட பகுத்தறிவாளர் ஒன்றியம் (DKRA) | 1976 |  India | Member of FIRA. |
| The Free Thought / De Vrije Gedachte (DVG) | 1856 | Netherlands | Focuses on atheism/secular humanism.[4] |
| Edinburgh Skeptics Society (EdSkeptics) | 2009 | United Kingdom | |
| European Council of Skeptical Organisations (ECSO) | 1994 |  Europe | A European umbrella organization, based in Roßdorf, Germany. |
| Federation of Indian Rationalist Associations / இந்திய பகுத்தறிவாளர் ஒன்றியங்களின் பேரவை (FIRA) | 1997 | India | Indian umbrella organisation. |
| Freedom From Religion Foundation (FFRF) | 1978 | United States | Focuses on state/church separation, nontheism, and atheism. |
| French Association for Scientific Information / Association française pour l'information scientifique (AFIS) | 1968[5] |  France | Member of ECSO.[2] |
| German Society for Fighting Quackery / Deutsche Gesellschaft zur Bekämpfung des Kurpfuschertums (DGBK) | 1903 |  Germany | Dissolved in 1934. |
| Glasgow Skeptics | 2009 | United Kingdom | |
| Good Thinking Society | 2012 | United Kingdom | |
| Het Denkgelag | 2012 | Belgium | |
| Hungarian Skeptic Society / Szkeptikus Társaság (HSS) | 2006 |  Hungary | Member of ECSO.[2] |
| Independent Investigations Group (IIG) | 2000 | United States | |
| Indian CSICOP | 19?? | India | Affiliated with CSI, member of FIRA. |
| Indian Rationalist Association (IRA) | 1949 | India | Member of Rationalist International. |
| Irish Skeptics Society | 2002 |  Ireland | Member of ECSO.[2] |
| Italian Committee for the Investigation of Claims of the Pseudosciences / Comitato Italiano per il Controllo delle Affermazioni sulle Pseudoscienze (CICAP) | 1989 |  Italy | Member of ECSO.[2] |
| James Randi Educational Foundation (JREF) | 1996 | United States | |
| Launceston Skeptics | 2010 | Australia | |
| Maharashtra Committee for Eradication of Blind Faith / Maharashtra Andhashraddha Nirmoolan Samiti (MANS) | 1989 | India | Member of FIRA. |
| Merseyside Skeptics Society (MSS) | 2009 | United Kingdom | |
| MTÜ Eesti Skeptik (skeptik.ee) | 2007 |  Estonia | |
| New England Skeptical Society (NESS) | 1996 | United States | Fusion of three earlier organisations. |
| New Mexicans for Science and Reason (NMSR) | 1990 | United States | |
| New Zealand Skeptics[6] (NZ Skeptics) | 1986 |  New Zealand | |
| Office for Science and Society (OSS) | 1999 | Canada | McGill University, Montreal. |
| Philippine Atheists and Agnostics Society (PATAS) | 2011 |  Philippines | |
| Polish Skeptics Club / Klub Sceptyków Polskich (KSP)[7][8] | 2010 |  Poland | |
| Portuguese Skeptical Community / Comunidade Céptica Portuguesa (COMCEPT) | 2012 |  Portugal | |
Rational Alternative to Pseudoscience – Society for the Advancement of Critical Thinking /
Alternativa Racional a las Pseudociencias – Sociedad para el Avance del Pensamiento Crítico (ARP-SAPC) | 1986 |  Spain | Member of ECSO.[2] |
| Rationalist Union / Union Rationaliste | 1930 | France | |
| Richard Dawkins Foundation for Reason and Science (RDFRS) | 2006 | UK &  US | The American and British branches are independent.
|
| Science and Popular Enlightenment / Föreningen Vetenskap och Folkbildning (VoF) | 1982 |  Sweden | Member of ECSO.[2] |
| Science and Rationalists' Association of India / Bharatiya Bigyan O Yuktibadi Samiti | 1985 | India | Based in Kolkata, West Bengal. |
| SKEPP[9] | 1990 | Belgium | Member of ECSO.[2] Serves Flanders and Brussels. |
| Skepsis ry | 1987 |  Finland | Member of ECSO.[2] |
| Skepsis Foundation / Stichting Skepsis (Skepsis) | 1987 | Netherlands | Member of ECSO.[2] |
| Skeptical Circle / Círculo Escéptico (CE) | 2006 | Spain | Member of ECSO.[2] |
| Skeptic Society / Общество скептиков[10] | 2013[11] |  Russia | |
| Skeptics in the Pub Online | 2020 | United Kingdom / World | |
| Society for the Scientific Investigation of Parasciences / Gesellschaft zur wissenschaftlichen Untersuchung von Parawissenschaften (GWUP) | 1987 |  D-A-CH | Based in Roßdorf, Germany. Member of ECSO.[2] |
| The Skeptics Society | 1992 | United States | Globally active, but mainly serves California. |
| Young Australian Skeptics (YAS) | 2008 | Australia | |
| Young Skeptics | 2015 | US | American after school program. |
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