The article introduces a method called ESTIMATE (Estimation of STromal and Immune cells in MAlignant Tumours using Expression data) to infer the fraction of stromal and immune cells in tumor samples based on gene expression data. ESTIMATE uses two gene signatures: a 'stromal signature' and an 'immune signature' to calculate scores that reflect the presence of each cell type in tumor samples. These scores are combined to estimate tumor purity. The method is validated using DNA copy number-based tumor purity predictions from The Cancer Genome Atlas (TCGA) and other public datasets. ESTIMATE shows significant correlation with tumor purity across different tumor types and platforms. The method is publicly available and can be applied to assess the presence of stromal cells and immune cell infiltration in tumor samples, providing insights into the tumor microenvironment and its impact on tumor biology.The article introduces a method called ESTIMATE (Estimation of STromal and Immune cells in MAlignant Tumours using Expression data) to infer the fraction of stromal and immune cells in tumor samples based on gene expression data. ESTIMATE uses two gene signatures: a 'stromal signature' and an 'immune signature' to calculate scores that reflect the presence of each cell type in tumor samples. These scores are combined to estimate tumor purity. The method is validated using DNA copy number-based tumor purity predictions from The Cancer Genome Atlas (TCGA) and other public datasets. ESTIMATE shows significant correlation with tumor purity across different tumor types and platforms. The method is publicly available and can be applied to assess the presence of stromal cells and immune cell infiltration in tumor samples, providing insights into the tumor microenvironment and its impact on tumor biology.