RNA extraction is a routine technique in a molecular biology lab. High quality of RNA extracted from plants is a prerequisite to succeeding in subsequent experiments such as reverse transcription-polymerase chain reaction, Northern hybridization, cDNA library construction, and microarray analysis. Two methods for RNA extraction in Arabidopsis , small-scale and large-scale, are described here. RNA isolated by using the small-scale method can be applied in most downstream applications. The large-scale RNA preparation is recommended to extract RNA for Northern hybridization only.