Solid Phase Extraction (SPE) is the most widely used method for the extraction, changing of solvents, clean-up, concentration and fractioning of organic compounds from clinical, biological, industrial, environmental, marine and food samples. However, most SPE procedures are still poorly developed with little consideration to the physics involved in the process and are described as a largely empirical, labour intensive and time consuming trial and error process, without much systematization. Here we attempt to throw the light on a lot of disagreements concerning the suitability of each sorbent for the extraction of a number of compounds, conditioning, washing off and elution protocols and regarding the recoveries achieved by a particular SPE protocol. This serious lack of systematization and homogenization makes difficult the efficient implementation of reliable SPE procedures. Particularly, this part is focused on the advantages and disadvantages of SPE vs Liquid-Liquid Extraction (LLE), controversies and contradictions found in literature as regards selection of sorbents, optimization of conditioning and elution protocols and recoveries by SPE. Moreover, it reveals the lack of selectivity of most of sorbents and SPE protocols and also includes the following sections: applications of SPE, fractionation by SPE, outlook and perspectives and conclusions.