Over the years the IAEA has provided advice to the Contracting Parties to the Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter (London Convention 1972) on the definition of de minimis levels of specific activity, below which materials can be regarded as ‘non-radioactive’ for the purpose of this Convention. The IAEA has prepared several documents elaborating the concept of de minimis for the benefit of the Contracting Parties. In 1999, the IAEA provided advice on the application of the principles of exclusion and exemption to sea disposal, which was adopted at the Contracting Parties’ Twenty-first Consultative Meeting. At the same meeting, the Contracting Parties adopted guidelines, which interpret the IAEA’s advice further and incorporate a Stepwise Evaluation Procedure to determine if candidate material can be designated as de minimis under the Convention. The final step in the Stepwise Evaluation Procedure involves a specific assessment to determine whether candidate materials for sea disposal contain de minimis levels of radioactivity. This publication has been prepared in response to a request by the Contracting Parties to the IAEA to provide additional guidance on how such specific assessments should be performed.