Portfolio rebalancing involves trading assets to maintain target allocations when market fluctuations cause drift outside target ranges. Tolerance band rebalancing uses bands around targets, only trading when allocations exceed bands. Interval rebalancing forces trades on schedules. Opportunistic rebalancing considers cash flows and tax implications. Rebalancing benefits include maintaining risk profiles and capturing gains, while costs include taxes and limiting growth. Rebalancing is part of a holistic approach to achieve long-term goals through disciplined processes.