The international version of other substantive areas, e.g. project finance, or international trade. Sometimes large corporate law firms have a substantial number of international clients and oversee business dealings between companies.
International law can intersect many aspects of the law.
For example, when you travel on a commercial airline flight there is the Warsaw Convention that limits the liability of the airline, in certain circumstances, for injuries that they may cause to you. An attorney for the US government could work with the US Trade Representative on negotiating a trade agreement with China. Also, a lawyer could work for Amnesty International and investigate claims against a foreign country. In addition, international lawyers are an integral part of the tribunal set up to investigate and prosecute war criminals in the conflict in the former Yugoslavia. Not to be copied or distributed without permission.