The present invention provides compositions and methods for preparing a nucleic acid library in a multi-purpose buffer (e.g., employing whole genome amplification), where nucleic acid purification is not required between or during steps. In certain embodiments, small amounts of starting nucleic acid (e.g., genomic DNA) are employed and the steps are accomplished in a single container. In some embodiments, the nucleic acid library is subjected to sequencing methodologies or rolling circle amplification.