In federal courts, even on claims governed by state law, costs are governed by 28 USC 1920. Since it states expressly that costs may be awarded in the district court’s discretion, section 1920 preempts state laws that award costs to the prevailing party as a matter of right. Here, the district court erred in applying such a Nevada law to award costs even though in the exercise of its discretion it would have denied costs to both parties.