Essential oils were obtained from leaf, branch and buds of Betula species: B. pendula Roth, B. browicziana A. Guner, B. litwinowii Doluch., B. recurvata V. Vassil., and B. medwediewii Regel naturally growing in various parts of Turkey. Also buds of the common birch B. pendula essential oil from Germany and two species native to Finland namely, Betula pubescens ssp. czerepanovii (Orlova) Hamet-Ahti and Betula pubescens ssp. pubescens Erhr. were investigated. Betula essential oils were obtained by different distillation techniques such as hydrodistillation, microdistillation and Likens-Nickerson simultaneous distillation-extraction method (SDE). The resulting volatile compositions were elucidated by gas chromatography ( GC) and gas chromatography-mass spectrometry ( GC-MS) systems. Known and new sesquiterpenes were isolated from Betula essential oils using column chromatographic techniques. Structure determination of each isolated compound was carried out using 1D and 2D NMR spectroscopic techniques supported by MS, UV and GC FITR. Biological activities were determined both for essential oils and pure compounds isolated from the oils of Betula species. Antifungal, antibacterial and antioxidant activity results were carried out using various in vitro techniques.