A configurable execution unit comprises operators capable of being dynamically configured by an instruction at the level of processing multi-bit operand values. The unit comprises one or more dynamically configurable operator modules, the or each module being connectable to receive input operands indicated in an instruction, and a programmable lookup table connectable to receive dynamic configuration information determined from an opcode portion of the instruction and capable of generating operator configuration settings defining an aspect of the function or behavior of a configurable operator module, responsive to the dynamic configuration information in the instruction.