We propose and demonstrate a novel thin film deposition technique by transferring the principles of atomic layer deposition (ALD), known with gaseous precursors, towards precursors dissolved in a liquid. The technique can also be considered as a generalization of already established methods such as the ‘layer by layer’ growth of polyelectrolytes, the ‘successive ion layer adsorption and reaction’ (SILAR), and even the solid-phase peptide synthesis. 'Solution ALD' (sALD) shares the fundamental properties of standard ‘gas ALD’ (gALD), in particular the self-limiting surface chemistry and the ability to coat deep pores in a conformal manner. Furthermore, standard gALD reactions behave similarly when transferred into sALD mode. However, sALD also offers novel opportunities by overcoming the need for volatile and thermally robust precursors. To illustrate this, we establish sALD procedures for depositing films of MgO based on the hydrolysis of a Grignard reagent, and of a polyamine exploiting a strategy of protection, deprotection and activation that is standard in organic synthesis. Those two examples highlight how ionic, polar, or high-molecular weight precursors that only exist in the condensed phase are now rendered amenable to being utilized in surface-controlled thin film formation by sALD for depositing materials that would otherwise be more difficult or more expensive to achieve by gALD.