What is the difference between organic and conventional food?

Germany

The (only) difference between organic and conventional food is the way how the food has been produced and processed. For instance, the use of fertilizers and pesticides is restricted in organic production.
Organic food is defined as the product of a farming system, which avoids the use of man-made fertilisers, pesticides, growth regulators and livestock feed additives. Instead, the agricultural systems rely on crop rotation, animal and plant manures, some hand weeding and biological pest control. "Organic" farming is the description used in English-speaking countries, whereas in other markets "Bio" or "Eco" are the more usual product descriptions.

The difference between "organic" and "conventional or traditional" foods is in the production. All food sold as 'organic' must be produced according to European laws on organic production. Although organically produced foods cannot be defined as pesticide free, the direct use of other than "traditional" agricultural chemicals is prohibited. One of the most commonly used fertilisers in organic production is manure. Farmyard manure is also used in conventional production methods. In both cases their use needs to be properly managed to reduce the risk of possible contamination of agricultural produce with pathogens (harmful bacteria, especially E. coli 0157) and to avoid the possible contamination of ground and surface waters.
There is no evidence that organically produced food is any safer, more nutritious than its conventionally produced counterpart.

Backgrounder on agriculture
http://www.eufic.org/en/quickfacts/food_agriculture.htm#07

To see what is allowed in organic farming in the EU and how it is defined see the COUNCIL REGULATION (EEC) No 2092/91 on organic production of agricultural products and indications referring thereto on agricultural products and foodstuffs:
http://europa.eu.int/eur-lex/en/consleg/pdf/1991/en_1991R2092_do_001.pdf