Long-term evolution of the state titles had needed some solutions for defining the interest rate in a more flexible manner. Considering that the state titles market is continuously developing, like the other titles markets, solutions have been found for increasing attractively. In the first part of this paperwork we will see that have been introduced state titles for which the interest rate is tide either to the official interest rate, either the price index of which attractive depends on the expressing rate of the interest rate: variable or fixed.