SOI vs. SOQ
An SOI is usually shorter and earlier in the process - enough for the agency to decide who is qualified and interested. An SOQ is a fuller qualifications package with deeper project sheets, resumes, and often a project understanding section. Some solicitations use the terms interchangeably; always follow the document the agency named.
Where SOIs show up
Local public agencies, state DOTs, and many municipal QBS processes solicit SOIs (or letters of interest) before ranking firms. Illinois and other state QBS frameworks commonly start with letters of interest or statements of interest, then evaluate and shortlist before negotiation.
How to write a strong SOI
- Mirror the advertised evaluation criteria in the order they appear
- Lead with the most relevant past projects - not the largest
- Name the key people who would actually do the work
- Stay inside any page or format limits; excess content is often discarded
What an SOI typically contains
Most SOIs are built from a few predictable pieces, kept intentionally brief. The point is to show the agency you are qualified and genuinely interested without burying reviewers in detail they did not ask for at this stage.
- A concise statement of the firm's interest in the specific project or contract
- Targeted relevant experience - a handful of projects that match the advertised work, not a full portfolio
- Key staff who would perform the work, with just enough detail to establish their fit
- Firm contact information and, where required, any registration or licensing basics the agency named
Where the SOI sits in the selection sequence
The SOI is usually the first step in a longer path. A common sequence is SOI, then shortlist, then a fuller SOQ or interview, then negotiation with the top-ranked firm. Because the SOI is what gets you onto the shortlist, its job is narrow: demonstrate enough qualification and interest to advance, not to win the whole selection. Details that belong in later stages - deep project sheets, full resumes, fee - are generally out of place here.
This staged approach is standard under qualifications-based selection, where agencies rank firms on qualifications before any discussion of price.
SOI vs. LOI vs. SOQ at a glance
| Document | Typical length | Where it fits | Level of detail |
|---|---|---|---|
| SOI (Statement of Interest) | Short | Early - to reach the shortlist | Concise interest, targeted experience, key staff |
| LOI (Letter of Interest) | Short | Early - often the same role as an SOI | Similar to an SOI; format is usually a letter |
| SOQ (Statement of Qualifications) | Longer | After shortlisting | Fuller project sheets, resumes, project understanding |
In practice an LOI and an SOI often play the same role; the difference is frequently just the label the agency chose.
Why brevity matters
An SOI is meant to be short, and there is usually a reason for that. Reviewers may be screening many firms quickly, and a solicitation that specifies a page or format limit expects you to respect it. A tight, focused SOI signals that you read the advertisement and can follow instructions - qualities the agency will weigh again at the SOQ and interview stages.
Common SOI mistakes
- Treating the SOI like a full SOQ and overwhelming reviewers with detail meant for later stages
- Ignoring stated page or format limits, which can get excess content discarded
- Leading with the firm's largest projects instead of the ones most relevant to the advertised work
- Including fee or price when it was not requested, which can hurt or disqualify a submission
- Listing staff who would not actually perform the work
For a worked example of how agencies run these early qualifications steps, see the local agency RFQ playbook.