Retirement Plans have lots of different notices that are required to be shared with participants. Unfortunately, all of this paper can be overwhelming at times. Here's a breakdown of what notices you might receive and what they mean.

Safe Harbor Notice —
Some plans have a special contribution called a "Safe Harbor" contribution. If you are receiving this notice, it means that your employer may make a special contribution to your account. You will receive this notice annually if it applies.
Automatic Contribution Arrangement (ACA) —
Some plans say that if you don;t choose your 401(k) contribution level, then the plan will choose a default contribution level for you (such as a deferral of 3%). This notice describes that arrangement and tells you how to make an affirmative election.
Qualified Default Investment Alternative (QDIA) Notice —
If you are in a plan that allows you to direct your assets, but you never completed an election form, then your plan contributions are invested in the default fund. Often the fund will be a QDIA and if so, then the plan is required to notify you that you are invested in the QDIA. This notice is required annually if it applies.
Fee Disclosure —
Legislation has mandated that if you can direct your investments (i.e. pick mutual funds that you want to invest in) for your plan, then you must receive certain information about those investments every year. The fee disclosure includes any expenses that are paid by plan assets that would affect your account. You may receive more than one of these notices as there may be fees that affect your account from multiple parties.
Comparative Chart —
The comparative chart shows information about all of the investment choices in your plan to allow you to see what choices are right for you. You will receive this information at least once per year.