Permutation nPr = n!/(n-r)! counts the number of ways to arrange r objects chosen from n distinct objects in a specific order. When r = n, nPn = n! gives total arrangements. When objects repeat — p of type 1, q of type 2, etc. — divide by p! * q! * ... to remove overcounting. For MISSISSIPPI: 11!/(4!4!2!1!) = 34650. Circular permutations fix one object to remove rotational symmetry: (n-1)! ways. If reflection symmetry also applies (necklace), divide by 2: (n-1)!/2. Restricted permutations require careful handling: objects always together (bundle as one unit, multiply by internal arrangements), objects never together (use gap method or complementary counting), objects in fixed positions (fix first, permute rest). JEE frequently asks word arrangement problems with conditions on vowels and consonants.