The ESV is based on the Masoretic text of the Hebrew Bible as found in Biblia Hebraica Stuttgartensia (5th ed., 1997), and on the Greek text in the 2014 editions of the Greek New Testament (5th corrected ed.), published by the United Bible Societies (UBS), and Novum Testamentum Graece (28th ed., 2012), edited by Nestle and Aland. The currently renewed respect among Old Testament scholars for the Masoretic text is reflected in the ESV’s attempt, wherever possible, to translate difficult Hebrew passages as they stand in the Masoretic text rather than resorting to emendations or to finding an alternative reading in the ancient versions. In exceptional, difficult cases, the Dead Sea Scrolls, the Septuagint, the Samaritan Pentateuch, the Syriac Peshitta, the Latin Vulgate, and other sources were consulted to shed possible light on the text, or, if necessary, to support a divergence from the Masoretic text. Similarly, in a few difficult cases in the New Testament, the ESV has followed a Greek text different from the text given preference in the UBS/Nestle-Aland 28th edition. Throughout, the translation team has benefited greatly from the massive textual resources that have become readily available recently, from new insights into biblical laws and culture, and from current advances in Hebrew and Greek lexicography and grammatical understanding.
Quoted from the Preface to the ESV at Crossway.org