It is commonly known that enzymatic transformations are considerably more specific than classical chemical reactions which usually lead to formation of byproducts. That is why the enzymes are a powerful tool in the field of analytical chemistry. The main problems occurring while working with enzymes stem from their relatively high price and sensitivity to non-physiological conditions. The above mentioned disadvantages may be overcome through enzyme immobilization which allows for reusing the biocatalyst as long as it retains its activity. When the immobilization is performed correctly the enzymes are more stable and also more resistant to denaturation. Such an approach in combination with additional benefits of miniaturization, heterogeneous catalysis and flow-mode operation contributes to the various applications of the Immobilized Enzyme Reactors (IMERs) in particular, microfluidic (mu-IMERs). In the present review various types of mu-IMERs were described. Particular attention was paid to techniques of their preparation including immobilization strategies and technical solutions connected with their applications using both capillary and chip format. (C) 2016 Elsevier B.V. All rights reserved.