How many points does one have to place on a unit square to guarantee that two of them are strictly less than 1/2 unit apart?
1. **Understanding the problem**: We need to determine the minimum number of points that must be placed on a unit square to ensure that at least two of them are strictly less than \( \frac{1}{2} \) unit apart.

2. **Optimal placement of points**: Consider placing points in a way that maximizes the minimum distance between any two points. One optimal way to place points is in a grid pattern.

3. **Placing 9 points**: Place 9 points in a \(3 \times 3\) grid within the unit square. The distance between adjacent points in this grid is \( \frac{1}{2} \) unit.

    \[
    \begin{array}{ccc}
    (0,0) & (0, \frac{1}{2}) & (0,1) \\
    (\frac{1}{2},0) & (\frac{1}{2}, \frac{1}{2}) & (\frac{1}{2},1) \\
    (1,0) & (1, \frac{1}{2}) & (1,1) \\
    \end{array}
    \]

4. **Minimum distance in this arrangement**: In this \(3 \times 3\) grid, the minimum distance between any two points is exactly \( \frac{1}{2} \) unit. This does not satisfy the condition of being strictly less than \( \frac{1}{2} \) unit.

5. **Adding one more point**: To ensure that at least two points are strictly less than \( \frac{1}{2} \) unit apart, we need to add one more point to the 9 points already placed. This additional point will force at least one pair of points to be closer than \( \frac{1}{2} \) unit.

6. **Conclusion**: Therefore, the minimum number of points required to guarantee that at least two of them are strictly less than \( \frac{1}{2} \) unit apart is \( 10 \).

The final answer is \( \boxed{10} \).