Bias insertion techniques are MC moves that have been designed to search the favorable energetic location, suitable cavities or distance-biased insertion holes 3 in the system to enhance sampling of ion insertion in water. An important example is the method of thermodynamic integration originally proposed by Kirkwood which is suited for calculations of free energies between two given states. In past work, it has been applied to the calculation of the chemical potential of ions in aqueous solutions. Its basic principle is the definition of a thermodynamic path where an ion is gradually added to the electrolyte solution by coupling its interaction with a scaling parameter λ, varying in the interval [0,1], during a MC or molecular dynamics (MD) simulation. Other advanced techniques such as multicanonical methods, metadynamics for chemical potential calculation or advanced configurational bias moves have been developed.