The Libertarian Party was included in this encyclopedia. I checked it out at a public library. Now, while it qualifies under the Author's contention that extremist parties are 'deviations from the normal' (my paraphrase), it shows the uselessness of such a definition of extremism.The Libertarian Party has never advocated the overthrow of the constitution, any state constitution, or any armed paramilitary activities. At most Libertarians may use their constitutional right to arm themselves, but it is on an individual basis without ANY organization by the party.The inclusion of the Libertarian Party makes the whole work suspect.