In this thesis, we study the static and dynamic Searchable Symmetric Encryption (SSE) schemes (Cash et al. (2014), Kamara and Moataz (2017)). We present different approaches for secure single- and multi-keyword ranked searches, that are: Sorted, OPEBased, Paillier-Based, Embedded, and Matrix-Based. We extend the base schemes according to these approaches so that the matching documents of a search query are ranked by a relevance score calculation technique like term frequency (tf), term frequency-inverse document frequency (tf-idf) or keyword frequency, depending on the characteristics of the scheme. For this, the existing structures of the schemes are modified since they cannot be directly used for ranked searches. Therefore, the ranking facility is added to them. Further, Matrix-Based Approach is a new hybrid approach that is based on an updated structure of the static scheme (Cash et al. (2014)) and fills a matrix to rank the relevant documents for a search keyword, as in the work (Ibrahim et al. (2012)), however, computing the matrix is totally different from their work.