This study examined the function of teiru in scientific books, focusing on its long-term progressive and perfective usages. Following Kyo (2000), this study categorized the progressive usage of teiru into two types: short-term progressive and long-term progressive. The first describes the progress of everyday actions, whereas the second presents a social or natural phenomenon or a writer's thoughts on a certain phenomenon. The perfective usage of teiru implies that the influence of a past event still remains in the present situation. In scientific books, the perfective usage is applied to quote a preceding study. In scientific books, long-term progressive and perfective teiru have the function of expressing a "topic of a paragraph" or "conclusion". When used at the beginning of a paragraph, teiru functions to establish the premise of an argument by presenting a thought, situation, or phenomenon before the discussion of the continuous part. And, at the end of a paragraph, teiru indicates the conclusion by expressing the thoughts and opinions of the writer or mentioning a social or natural phenomenon. The reason why these usage of teiru are used to express the "topic of a paragraph" or "conclusion" is that the long-term progressive or perfective usage of teiru can express a theory, thought or general phenomenon. The perfective usage shows the assumption of a topic or a conclusion by quoting a preceding study. The unifying topic in the perfective usage of teiru acts to relate a topic, an argument, and a conclusion to each other.