Your wife's 40th birthday only happens once. Turning 40 years old is a milestone birthday that older adults may never forget. Let your wife know how special she is to you and her friends by planning a memorable birthday celebration. Spend some time thinking about your wife's personality and what type of party she would enjoy to mark the occasion.

Your wife may be expecting a big birthday celebration in honor of her 40th birthday. Tell her you think a small party would be more intimate, then secretly plan a big surprise party. Use a social networking site or personal email account to invite friends and family. Enlist the help of a friend and ask her to take your wife shopping while the guests arrive at the party. Plan the birthday on an unexpected day, such as the middle of the week or a few days before her birthday. Have the party catered or ask family to make some healthy foods and your wife's favorite flavor of cake. When your friend brings your wife back, hide and yell "Surprise" when she walks in.

Whisk your wife away on a memory trip in honor of her 40th birthday. The trip does not need to be expensive or lengthy. Focus on recreating some special memories of your wife's life. Several months before her birthday ask her questions about special memories she has from each decade of her life. If possible, visit or recreate those events and places. For example, you may visit her childhood home, her high school, where the two of you met and the location of your wedding. Put together a pictorial scrapbook with photos of special times and look through the book on your trip. This memory trip birthday will be one she never forgets.

Dan Balz, in a 2006 article titled "Bill Clinton's 60th Birthday Benefit Blowout," published in "The Washington Post," highlighted a useful idea that you can use for your wife's 40th birthday celebration: throw her a benefit party. By her 40th birthday, your wife may have causes she is passionate about. She may support those causes financially and by volunteering. Instead of presents, ask the guests to make a donation to your wife's favorite charity in her honor. Expand the invitation list to include out of town guests who cannot attend the celebration but would be willing to donate in your wife's name. Decorate with streamers and balloons in the charity's colors and have a matching cake made.

Your wife may not be as excited as you are to celebrate her 40th birthday. If that is how she feels, plan an "unbirthday" party and celebrate in the style of the classic novel, "Through the Looking Glass," by Lewis Carroll. Have a baker make a lopsided cake complete with playing cards and brightly colored candles. Cut out sandwiches in the shape of umbrellas or odd shapes. Play the soundtrack from the movie. Ask the guests to bring unusual birthday presents rather than the traditional candles, gift certificates and jewelry. If asked for suggestions, mention some of your wife's unusual collections or hobbies.