Promotion

Max begins every career at Rank 099. At the end of any mission, assuming Max has gathered enough Points, he will receive a Promotion from the CIA Chief. This increases his current rank by a certain number of levels, potentially reaching Rank 001 if sufficient points are collected throughout his career.
Ranks have absolutely no impact on gameplay. They simply indicate the accumulating success of Max's career. It is possible to complete the game without reaching Rank 001, especially due to poor performance as well as on low Difficulty levels.
==Max's Rank==
When Max is initially created, he holds a Special Agent Rank of 099. This is the "lowest" rank possible.
Each time a Mission is concluded, the games tallies a Score based on Max's performance during that mission. This is added to the total tally of points Max has earned so far throughout his entire career.
When specific quotas are reached, Max will be Promoted by the CIA Chief, immediately after the Weekend Cutscene is displayed. Assuming he continues gaining points, Max can slowly climb the rank ladder. His rank number will gradually "decrease" from 099 towards 001, assumably indicating that he is "surpassing" other CIA Super Agents in his performance.
There is no way to "lose" rank, I.E. for the rank number to increase back towards 099. Failure to earn any points during a mission simply does not increase Max's advancement towards the next rank.
Also, regardless of how many points Max manages to earn throughout his career, he can never surpass Rank 001.
==Significance==
Max's rank has no bearing on gameplay whatsoever. It is strictly a measure of success that spans Max's entire career. Mostly this is done in comparison to the number of Missions Max has played so far. In other words, reaching Rank 0XX after Y missions indicates better gameplay than reaching the same rank after y+1 missions.
Unfortunately, there is no built-in way to compare ranks between careers. This is mostly a bragging-rights reward, or a way for the player to measure his own ability in playing the game.
==Point Quotas==
Each time Max has gathered a certain number of points - a Quota - he will reach a specific rank. For example, once Max has acquired a career-total of 400 points, he will immediately be promoted to Rank 080. This occurs regardless of whether he previously was Rank 099 or Rank 081 - reaching the set number of points yields a set level. This is similar to many experience-based Role Playing Games, where each "level" requires accumulating a set number of experience points.
The "distance" between the point quotas for each rank and its next higher rank increase as you get nearer to rank 001. In other words, you will need a small number of points to go from rank 099 to 098, a larger number of points to go from rank 080 to 079, and a significantly larger amount of points to go from rank 002 to rank 001. Therefore, early in his career Max may skip forward several ranks simply by completing a single mission, but later might need to complete several missions to gain enough points to advance a single rank.
The formula for determining the point quota for each rank is probably too complex to print out. However it does seem that the following rules apply:
*You will gain your first rank (099->098) once 48 points have been earned.
*You will gain an additional rank for each 16 points accumulated beyond 48, until Rank 090. 16 points are roughly equivalent to the Arrest of a single low-ranking enemy agent (again, on the lowest difficulty setting).
*Beyond Rank 090, you will need 32 or 16 points (alternating) to advance from one level to the next, until rank 080.
*Beyond Rank 080, you will need 32 points for each rank advancement, until rank 070.
*This continues, gradually doubling the amount of required points every few levels. So you will eventually need 64, then 128, then 256 points and so on to advance from one rank to the next. Also, the frequency of this "doubling" effect increases as you advance.
*Soon enough you will reach a situation where even a highly-successful mission does not grant enough points to advance in rank.
*The required number of points to go from level 005 to 002 is estimated at around 30000 points. This is equivalent to 10 missions completed "perfectly" at Regional Conflict difficulty, or about 6-7 missions completed "flawlessly" (by Turning all enemy agents) at the same difficulty.
*It is also estimated that a career-wide total of around 65000 (possibly 65535) points are required to attain rank 001.
Remember that if a single mission has earned you a large enough number of points, you can skip several ranks during the same promotion. The only thing the game cares about is how many points you've gathered so far during your career, then bumps you to the rank corresponding to that amount.