Long intergenic noncoding RNAs (lincRNAs) transcribed from intergenic regions of yeast and animal genomes play important roles in key biological processes. Yet, plant lincRNAs remain poorly characterized and how lincRNA biogenesis is regulated is unclear. Using a reproducibility-based bioinformatics strategy to analyze 200 Arabidopsis transcriptome datasets, we identified 13,230 intergenic transcripts of which 6,480 can be classified as lincRNAs. Expression of 2,708 lincRNAs was detected by RNA-seq experiments. Transcriptome profiling by custom microarrays revealed that the majority of these lincRNAs are expressed at a level between those of mRNAs and pri-miRNAs. A subset of lincRNA genes show organ-specific expression whereas others are responsive to biotic and/or abiotic stresses. Further analysis of transcriptome data in 11 mutants uncovered SERRATE, CBP20, and CBP80 as regulators of lincRNA expression and biogenesis. RT-PCR experiments confirmed these 3 proteins are also needed for splicing of a small group of intron-containing lincRNAs.