Index -> Playing the Game -> Planning Phase -> Playing Cards -> Tech Cost
To play a card, you must have enough available tech to pay its tech cost. You may play as many cards as you like each turn, subject to the limitations of your available tech. Your Tech Status will update to show you how much remaining tech you have to play cards as you assign/unassign cards. If you are trying to play a card that won't seem to target, check your Tech Status - you might not have enough tech to play it this turn.
Your tech is fully restored at the start of each turn. Unspent tech does not accumulate from one turn to the next.