Oil and gas production from unconventional reservoirs (i.e. tight) now accounts for about half of the total US hydrocarbon production from essentially zero ten years ago. Such a drastic increase in production from unconventional resources was made possible by combining horizontal drilling and hydraulic fracturing. More than 15,000 horizontal wells per year have been drilled and hydraulically fractured in unconventional reservoirs (oil and gas) since the mid-2000s. It is typical to design for 60 to 100 hydraulic fractures to be placed over a well length of about 5,000ft (with spacing between fractures of 30 to 100 ft). In order to reduce operations cost, the completion of the well is performed in “stages”, with one pumping stage aiming at placing a number of hydraulic fractures simultaneously (typically between 2 to 6). Although, such a “plug & perf” multi-stages completion technique has allowed tremendous cost savings, its overall efficiency and robustness remains doubtful: about 30% to 40% of the fractures are typically found not contributing to well production at all. In this talk, we will review the basics of hydraulic fracturing operations and its mechanical modeling (e.g. viscosity versus toughness dominated regime of propagation of hydraulic fractures, fracture height containment etc.). We will then present theoretical and field evidences of the difficulties associated with multi-stage “plug & perf” fracturing as it is performed today. Opportunities for improvement in a number of area (materials and structures used downhole, processes etc.) will be discussed, highlighting the important role that the mechanical community has to play in further enhancing hydrocarbon production from unconventional reservoirs.