europa.eu/legislation_summaries/internal_market/living_and_working_in_the_internal_market/free_movement_of_workers/index_en.htm
This is another section of the Europa website containing detailed links leading to the free movement of workers. It also contains information about Directive 2004/38/EC.

ec.europa.eu/internal_market/top_layer/index_19_en.htm
This is a section within the Europa website giving comprehensive information about the freedom of establishment. This site is excellent as it contains links for the different principles in this area and also a link for the cases of the European Court of Justice in this field.

www.wcl.american.edu/journal/lawrev/53/rothe.pdf?rd=1
This is a comprehensive essay on the freedom of establishment in the EU.

www.oru.se/oru-upload/Institutioner/BeteendeSocialR%E4ttsvetenskap/Dokument/Rattsvetenskap/Art%2039%20EC%20and%20the%20free%20movement%20for%20.pdf
This is a comprehensive article entitled "Article 39 and the free movement for economic active persons" citing the leading case of Bouchereau which was adopted into Article 27(1) of the 2004/38/EC Directive.