This paper is co-authored by an informal group of experts from a broad range of backgrounds, all of whom are active in standards groups, consortia, alliances and/or research projects in the Internet of Things (IoT) space. This paper has two objectives: 1) explain the need for semantic interoperability, 2) provide recommendations for semantic interoperability standards using ontologies. The target audience for this paper are: ● IoT system product owners who need to understand how they can effectively ensure interoperability of their products. ● IoT system and standardization engineers without background in semantic technologies. The document is made available under the ​Creative Commons Attribution 4.0 International License​.