Evergreen date guide

What is celebrated on April 11?

See the observances and verified observance-history milestones attached to April 11. Each observance keeps its own source and date details.

Verified history

On this date in observance history

Today in history →

Selected observance milestones connected to this date, based on reviewed sources.

2022

First observance

Marketing Operations Appreciation Day

Zapier describes the 2022 event as the first Marketing Ops Appreciation Day.

2021

First observance

National Ranch Water Day

The observance was created in February 2021 and recurrence directories record annual April 11 observance beginning in 2021.

1997

First observance

World Parkinson's Day

Parkinson’s Europe first-edition historical account gives exact inaugural date.

About this date

What this date contains

10 observances

Each observance is shown once in this view, with its own source and scope details available on the guide page.

0 repeat predictably

0 use a fixed annual date and 0 follow a reusable calendar rule.

0 are edition-specific

These dates are shown only for the year or edition that has been confirmed.

4 have a country-specific scope

Country-specific observances are not presented as worldwide events.

10 have in-depth guides

These pages include reviewed meaning, history, activities, facts and FAQs.

Reviewed depth

Other in-depth guides on April 11

Source-backedFixed AnnualIn-depth guide

Dog Therapy Appreciation Day

11 April · Informal pet/therapy-animal appreciation calendar usage documented by a veterinary institution

The Animal Medical Center repeatedly lists Dog Therapy Appreciation Day on April 11 in annual pet-awareness calendars.

Source-backedFixed AnnualIn-depth guide

Día de la Batalla de Rivas

11 April annually · Costa Rica / statutory national commemoration

Costa Rica Legislative Assembly and cultural-history sources verify April 11 as the annual Battle of Rivas commemoration, the April 11, 1856 historical anchor and Act 8886 later date-protec…

Source-backedFixed AnnualIn-depth guide

International Louie Louie Day

11 April in the organizer/community tradition; current activity should be rechecked yearly · Grassroots music/fan observance centered on the song “Louie Louie”

The Louie Louie advocacy/fan community documents International Louie Louie Day and its April 11 tradition, developed through the Louie Louie Advocacy and Music Appreciation Society ecosyste…

Source-backedFixed AnnualIn-depth guide

Marketing Operations Appreciation Day

11 April · Professional/workplace / Zapier-created Marketing Operations Appreciation Day

Zapier’s own 2023 campaign page states that Marketing Operations Appreciation Day is April 11 and describes it as an annual recognition initiative.

Source-backedFixed AnnualIn-depth guide

National Barbershop Quartet Day

11 April · Barbershop Harmony Society / organized barbershop commemoration

The Barbershop Harmony Society says National Barbershop Quartet Day commemorates the birth of the organized barbershop movement on 11 April 1938.

Source-backedFixed AnnualIn-depth guide

National Cheese Fondue Day

11 April · United States / informal food observance repeatedly promoted by The Melting Pot

The Melting Pot’s first-party 2025 material identifies April 11 as National Cheese Fondue Day, continuing a long-running brand celebration.

Explore the mix

Topics represented on April 11

All topics →

Arts, Entertainment & Lifestyle 3 Workplace, Professions & Appreciation 2 Food, Drink & Hospitality 2 Civic, Remembrance & History 1 Animals, Nature & Environment 1 Health, Wellness & Awareness 1

10 observances

All observances on this date

Source-backedFixed AnnualIn-depth guide

Dog Therapy Appreciation Day

11 April · Informal pet/therapy-animal appreciation calendar usage documented by a veterinary institution

The Animal Medical Center repeatedly lists Dog Therapy Appreciation Day on April 11 in annual pet-awareness calendars.

Source-backedFixed AnnualIn-depth guide

Día de la Batalla de Rivas

11 April annually · Costa Rica / statutory national commemoration

Costa Rica Legislative Assembly and cultural-history sources verify April 11 as the annual Battle of Rivas commemoration, the April 11, 1856 historical anchor and Act 8886 later date-protec…

Source-backedFixed AnnualIn-depth guide

International Louie Louie Day

11 April in the organizer/community tradition; current activity should be rechecked yearly · Grassroots music/fan observance centered on the song “Louie Louie”

The Louie Louie advocacy/fan community documents International Louie Louie Day and its April 11 tradition, developed through the Louie Louie Advocacy and Music Appreciation Society ecosyste…

Source-backedFixed AnnualIn-depth guide

Marketing Operations Appreciation Day

11 April · Professional/workplace / Zapier-created Marketing Operations Appreciation Day

Zapier’s own 2023 campaign page states that Marketing Operations Appreciation Day is April 11 and describes it as an annual recognition initiative.

Source-backedFixed AnnualIn-depth guide

National Barbershop Quartet Day

11 April · Barbershop Harmony Society / organized barbershop commemoration

The Barbershop Harmony Society says National Barbershop Quartet Day commemorates the birth of the organized barbershop movement on 11 April 1938.

Source-backedFixed AnnualIn-depth guide

National Cheese Fondue Day

11 April · United States / informal food observance repeatedly promoted by The Melting Pot

The Melting Pot’s first-party 2025 material identifies April 11 as National Cheese Fondue Day, continuing a long-running brand celebration.

Source-backedFixed AnnualIn-depth guide

National Pet Day

11 April · United States-origin / creator-led pet observance with public-institution recognition

Founder Colleen Paige’s current holiday list places National Pet Day on April 11, and the U.S. Census Bureau lists National Pet Day on April 11 in its current April resources.

Source-backedFixed AnnualIn-depth guide

National Ranch Water Day

11 April · United States / RANCH2O Spirits-created beverage observance

RANCH2O Spirits currently states that it gave Ranch Water a national holiday and publishes April 11; the creator-submitted National Day Archives record dates creation to February 2021 and a…

Source-backedEdition SpecificIn-depth guide

Slow Art Day

11 April 2026; 3 April 2027 · Slow Art Day organizer / global museum and gallery event

Slow Art Day says Phyl Terry developed slow-looking experiments in 2008–2009 and then launched Slow Art Day with a volunteer team; the organization describes the event as founded in 2010 an…

Source-backedFixed AnnualIn-depth guide

World Parkinson's Day

11 April · Organizer-backed international observance

Parkinson's Europe and the international Parkinson’s community

How dates are selected

This page combines fixed annual dates, reusable calendar rules and year-specific dates confirmed for 2026. Variable or historical dates are included only when they are clearly supported.

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