A few years ago, the social media world celebrated "Thank a Nun Day". The internet was full of pictures, with the hashtag #ThankaNunDay. I thought, "It's about time!"

Quite often in the missions, it is the Sisters who are in the trenches. We hear their stories or see their work: these women who have given their lives to God in service to others are true heroes.

This point was driven home by a man I once heard speak at a fundraising dinner. He talked of becoming involved with medical missionaries early in the HIV/AIDS crisis in Africa. It was a huge struggle, logistically and financially, to bring proper treatments to remote areas affected by the virus. Added to this problem was the issue of trust -- well-meaning outsiders, doctors and nurses, were arriving in areas where education was limited and refrigeration sometimes non-existent. The medical staff would tell people that the medicine had to be kept cold and taken at exact times in specific doses. Sometimes the details were overwhelming, and people hesitated to trust strangers.

The solution? They put the drugs into the hands of the Sisters serving the communities. When told the complicated regimen of times and dosages by the Sisters, the local people responded as we all would: "Yes, Sister." And then, they complied.

After the 2010 earthquake in Haiti, Sisters were on the forefront of relief efforts. A good friend of this office, Sister Lisa Valentini, MSC, tells of traveling through the Dominican Republic to reach the epicenter of the tragedy, Port-au-Prince, with sisters representing many orders. They came from all over the world with one goal -- service.

The Sisters quickly assessed the needs and began to work, helping where they could. Since Sister Lisa is a teacher, she was charged with keeping the children engaged, utilizing what had been donated -- crayons and coloring books. At one point, she found herself acting as an art easel with little ones leaning on her arms, legs, back, and even her head so they could draw!

One sister -- a nurse -- came from Spain. She left her paying job at a hospital to join the relief efforts. This meant that the elderly sisters with whom she lived would be without her salary as she took a leave of absence from her work. Though they counted on the income for their daily bread, the retired Sisters voted to sacrifice and fast, eating mostly potatoes for months, while Sister Carmen worked where she was most needed.

Heroic service wherever they are needed? Indeed.

Say it with me: "Yes, Sister."

Thank you, Sisters!

- Maureen Crowley Heil is Director of Programs and Development for the Pontifical Mission Societies, Boston.