In this work, ionic liquids are evaluated for the first time as solvents for extraction and entrainers in separation processes involving terpenes and terpenoids. For that purpose, activity coefficients at infinite dilution, γ13 ∞, of terpenes and terpenoids, in the ionic liquids [C4mim]Cl, [C4mim][CH3SO3], [C4mim][(CH3)2PO4] and [C4mim][CF3SO3] were determined by gas−liquid chromatography at six temperatures in the range 398.15 to 448.15 K. On the basis of the experimental values, a correlation of γ13 ∞ with an increase of the solubility parameters is proposed. The infinite dilution thermodynamic functions were calculated showing the entropic effect is dominant over the enthalpic. Gas−liquid partition coefficients give indications about the recovery and purification of terpenes and terpenoids from ionic liquid solutions. Presenting a strong innovative character, COSMO-RS was evaluated for the description of the selectivities and capacities, showing to be a useful tool for the screening of ionic liquids in order to find suitable candidates for terpenes and terpenoids extraction, and separation. COSMO-RS predictions show that in order to achieve the maximum separation efficiency, polar anions should be used such as bis(2,4,4-trimethylpentyl)phosphinate or acetate, whereas high capacities require nonpolar cations such as phosphonium. ; This work was developed in the scope of the projects CICECOAveiro Institute of Materials (ref. FCT UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when applicable cofinanced by FEDER under the PT2020 Partnership Agreement, and LSRE/LCM FCT UID/EQU/ 50020/2013). M.A.R.M thanks FCT for the Ph.D. grant SFRH/ BD/87084/2012, to COST for the STSM Grant from COST action CM1206 and to Andrzej Marciniak and Michał Wlazło for the laboratorial support. B.S. acknowledges FCT for the award of the postdoctoral grant SFRH/BPD/38637/2007 and the award of the research project PTDC/AAC-AMB/121161/2010.