A country may become a party to a treaty through more than one path. One path is to sign the treaty during the period in which the treaty is open for signature and then to ratify the treaty. However, country may also become a party by acceding to or by accepting the treaty.
When a country becomes a signatory to a treaty, it declares its intention to make the terms of the treaty legally binding on itself, but the act itself does not make that act binding. When a country ratifies a treaty, it makes the terms of the treaty legally binding, once the treaty’s requirements for entry into force are met.
For example, the U.S. has signed the Kyoto Protocol, but not ratified it. The Kyoto Protocol is not binding on the U.S.
Members of the European Union have both signed and ratified the Kyoto Protocol; when the Kyoto Protocol meets the minimum requirements for entry into force, the protocol will be binding on them. Kyoto has not yet met those requirements, however, so Kyoto is not legally binding on any country.