The membrane separation processes offer a number of advantages in terms of low energy use and capital investments. Polymers are most important available materials used to fabricate membranes. Polymers are modified to achieve tailored properties. This book gives a systematic presentation of modification of polymers by blending to improve the performance of cellulose acetate and poly sulfone membrane with sulfonated poly (ether ether ketone) (SPEEK) and pore forming modifier poly ethylene alcohol. The modified membranes are applied for the separation of bio molecules and toxic heavy metal ions. Distinguishing Features are Fabrication of polymeric blend membranes by phase inversion process, Studies on applicability of membranes for the separation of toxic heavy metal ions such as Cu, Zn, Cd, and Co from aqueous solutions. The book is intended primarily for undergraduate, postgraduate, researchers of chemical engineering and materialist in science and engineering. Some of the research findings discussed would also greatly benefit students and researchers who wish to specialize in certain areas and those in industry engaged in separation and purification technology research.