This paper deals with the issues of corpus annotation and sentiment analysis. Authors choose blogs for sentiment analysis, since blogs constitute an ideal resource for the constitution of an annotated corpus bringing together the subject and the sentiment expressed about the subject. Adopting the Charaudeau’s theory (1992) about opinion-evaluation for the French language, the authors describe the manual annotation of the opinions-evaluation in the Blogoscopy corpus, a corpus of French blogs. The annotation of the corpus is governed by a theoretical, a practical and a methodological principle, which are described thoroughly.